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Apple announced two new models of the Apple TV 4K (3rd Gen). We’ve added details in What to look forward to.

When placed around a living space, these low-profile wireless devices are able to detect specific activities, like movement, temperature, or the opening or closing of a door. Then they tell other smart devices how to react—smart lights, plugs, speakers, thermostats, and so on—all in an instant, and without requiring any direct commands or effort from you. Some detect just one activity, while others are multitaskers. Install one and you might solve a single problem—add a bunch and you’re on your way to having a home that runs on autopilot.

You might install a motion sensor at the top of a stairway and then, using an app, instruct it to turn on a light downstairs whenever someone walks by at night. If you want to take it to the next level, you might program it so in the morning it tweaks the thermostat, and then starts playing music when you come downstairs. A contact sensor on an exterior door might be used to alert you whenever an Airbnb tenant arrives, or perhaps if the back door has been left open at night. And a temperature sensor in a child’s room (or a chicken coop) can alert you if it gets too hot, cold, humid, or dry, and if you like, even have it adjust a fan or the thermostat automatically. “To get a smart home, you need sensors,” said Mitch Klein, executive director of the smart-home technology group Z-Wave Alliance.

For this guide we tested a few dozen smart sensors that are compatible with three of the most popular DIY smart-home systems: Amazon Alexa, Apple HomeKit, and Samsung SmartThings (Google Home, while popular, has yet to offer meaningful support for smart sensors). Those systems, often called “platforms,” are controlled by their own app and are important because they let you connect your smart sensors with other smart devices, and then customize how they all work together.

Below you’ll find our favorite picks, plus a few good alternatives, for the three major types of smart sensors: motion, temperature, and contact.

I’ve been a journalist for more than two decades and focus on the smart home and connected living. Since 2016 I’ve spent countless hours testing smart-home gadgets for Wirecutter, including smart thermostats, smart garage-door controllers, smart sprinkler controllers, and smart smoke alarms. I’m also a contributor to Dwell, U.S. News & World Report, BBC, and The Ambient, among others.

In researching this guide I spent two years living with smart sensors triggering lights, locks, music, thermostats, and more throughout my home, much to my family’s annoyance.

Smart sensors are a great option for everyone from smart-home newbies to devout enthusiasts. At the most basic level, these small, battery-powered devices offer simple solutions to common problems. Often forget to shut the garage door? Use a contact sensor to send a notification to your phone when it’s been open for more than a reasonable time. Have a toddler that’s just learned how to climb out of her crib? Put a motion sensor in the room and get alerted whenever she’s going rogue.

Smart sensors have a lot more potential than that though, and when a few are distributed around a home and linked up to other devices, they can transform that space from a place that has a bunch of smart-home gadgets to a smart home—where your devices work together, often autonomously.

Besides the convenience and wow factor, smart sensors are an excellent tool for saving energy around the home. A motion sensor can tell smart bulbs and switches, speakers, and a television to automatically turn off when a room is empty for too long or at a set hour every night. Contact sensors on doors and windows can signal a smart thermostat to shut off when they’re opened and turn back on when they’re closed. A temperature sensor can trigger shades to lower when a room is getting too warm on a sunny afternoon.

Sensors need to be set up using a smartphone app, and there are several software ecosystems—often called platforms—you can use with them that in turn are compatible with a whole bunch of devices made by a whole bunch of different companies. (The most popular platforms include Amazon Alexa, Apple HomeKit, Google Home, and Samsung SmartThings; IFTTT is another service that allows you to automate devices from different companies, which we explain in This App Turns Any Smart Device Into a Multitasker.) These platforms are great because they allow you to consolidate the controls of all (or most of) your smart devices into a single app, and they also bring perks like voice control when used with smartphones, smart speakers, smart displays, and tablets. They also let you configure your sensors to trigger other devices, using what are called Routines, Scenes, and Automations. The choice of smart platform is up to you, however if you already use an Amazon Alexa device or an Apple HomePod speaker, you might consider sticking with the platform they support. In addition to discussing sensors that work with smart-home platforms, we included in this guide a few sensors that work with their own app, as well as some that work with multiple platforms, so you don’t have to be locked into just one.

Most sensors communicate over Z-Wave or Zigbee wireless signals (though a few may use common Bluetooth or Wi-Fi, too.) The advantage is that they’re especially energy efficient and therefore support long battery life; they also create a mesh wireless connection, which means each device shares its wireless connection with the sensors closest to it. This way nothing goes out of range—a huge issue you’ve probably experienced if you can’t get on Wi-Fi in certain corners of your home. The downside is that these sensors may also require that you use a device called a hub or bridge, which acts like a mediator between your sensors and your home Wi-Fi network (some smart speakers also function as hubs).

Even though sensors that use Bluetooth or Wi-Fi don’t require a hub, we generally don’t recommend them because they don’t work anywhere near as reliably. In our testing, Wi-Fi sensors react more slowly, drain batteries faster, and are much bigger and more obtrusive than sensors that use less power-hungry protocols. Bluetooth sensors fare slightly better but have significant range issues and don’t work well if they aren’t near your phone. A new wireless protocol, Thread, combines the benefits of all these wireless protocols with none of the drawbacks. But it has very limited availability (see What to look forward to for more on this).

Many smart devices are capable of doing way more cool things than they advertise. The free service IFTTT makes it easy to set them free.

In deciding which smart sensors to test we focused on those that can make your home run on autopilot, which led us to motion, contact, and temperature sensors. If you’re interested in sensors for home security, see our guide to the best home security system. We also cover other environmental sensors in our guides to the best smart smoke alarm and the best smart water-leak detector.

For maximum convenience we prioritized sensors that were compatible with at least one of the three largest smart-home ecosystems: Amazon Alexa, Apple HomeKit, and Samsung SmartThings. We also restricted our search to devices that had strong user and professional reviews, as well as any we had selected in the past in the three existing guides to smart sensors (this guide is a consolidation of those previous guides).

To test our sensors, we installed them in a four-bedroom, 2,500-square-foot home that has three floors and three exterior doors. Using an iPhone XS Max we set up similar routines and actions for each device in each compatible ecosystem and went about daily life with a family of four people and one 60-pound dog. During that time, we recorded the following:

Reliability: We noted how consistently sensors were able to trigger Routines and Automations. Range: We tracked how far from the hub or router a sensor could be placed and continue to work reliably. Response time: We looked at how quickly or slowly a sensor detected and then was able to trigger other devices. Setup and installation: We considered how easily a device could be installed and paired with a smart-home platform. Pet immunity: We monitored whether pets would accidentally trigger motion sensors. Battery life: We tracked longevity over two years in most cases, as short battery life triggered the biggest number of complaints in user reviews (especially since some of those small batteries are really expensive!).

We also evaluated the design, build quality, size, and mounting options as top priorities. Our assumption was that anyone interested in home automation would plan to install multiple sensors throughout their home, so price became a serious factor as we made our picks. Spending $40 or more on a contact sensor for every door in a house would add up very quickly.

Wirecutter takes security and privacy issues seriously. As part of our vetting process, we look at the security and data privacy practices behind our product picks. We also have the companies that produce our top picks answer specific questions around their security and privacy policies. Here are the results.

Is a username and password required to use the device?

Does the app offer two-factor authentication? If so, is it required?

Is user data encrypted in the cloud?

Is a user's identifying data (such as their email address or Wi-Fi info) encrypted when stored in the cloud?

Can the device be used locally, or is a cloud connection needed?

Do you share data with third parties?

Does the device record and share location data?

Does the device offer tamper alerts in case of theft?

Worry that your smart-home devices may be acting sneaky? So do we. Our reviews dig into privacy and security so you can feel better about our recommendations.

A motion sensor detects when something crosses its path and can be used to turn on smart lights whenever someone enters a room. But it can also trigger an Automation or Routine, which will cause one or more smart devices to react. For example, you can set a motion sensor in the upstairs hallway so that anyone passing by between 6 p.m. and 9 p.m. will trigger the hallway lights to turn on, the thermostat to lower, and the front door to lock.

For lighting applications, some motion sensors are more effective than basic occupancy sensors. A good motion sensor has a lux (light level) sensor built in, so that you can set it not to trigger lights if the room is bright enough already. You can use them to set the system to come on after motion is detected at a specified light level based on the time of day—say, dimmed in the evening, brighter in the morning. Motion sensors can also trigger based on the lack of motion, so that lights will turn off if no one is in the room. Conveniently, these sensors can be mounted to a wall or set on a flat surface, making them easy to place throughout your home.

Reliable, really cheap, and flexible to mount, the Aqara motion sensor works with HomeKit and Alexa, but does require a hub.

Compatibility: Amazon Alexa, Apple HomeKit, IFTTT

The Aqara Motion Sensor works reliably, is very small, easy to install, and yet costs just $20 (a newer version is now available; check out What to look forward to for details). Though it uses a Zigbee wireless signal and works with both Amazon Alexa and Apple HomeKit, it can’t connect to them directly and needs an Aqara hub to connect to either platform, which at least helps boost wireless range (there are three hub models: The Aqara Hub M1S plugs directly into an outlet; the Aqara Hub M2 plugs into a router; and the Aqara Camera Hub G2H doubles as a camera).

The Aqara Motion Sensor has two parts: the sensor and an optional adjustable mount, so you can install it on a wall or ceiling, or simply place it on a flat surface. In our testing, the motion sensor turned on Philips Hue bulbs in our living room within a second of entering. The included button battery (a CR2450) was still going strong after a year of testing.

The Aqara Motion Sensor can’t be paired directly with Alexa. You need to use Aqara’s slightly wobbly app to pair the devices to an Aqara hub and then to pair the hub to Alexa. The hub and sensor can be paired directly to HomeKit, however, without the use of the Aqara app.

Although it’s bigger and pricier than our pick, this reliable sensor works with SmartThings or Zigbee-enabled Echo speakers without a hub.

Compatibility: Amazon Alexa (Zigbee-enabled speakers only), Samsung SmartThings, Zibgee hubs

The Centralite Micro Motion Sensor is also inexpensive and a good option if you are already using Samsung’s SmartThings platform; it can also pair directly to any Zigbee-enabled Alexa smart speaker in lieu of using a hub (see FAQs for a deeper explanation). In our testing it is larger and more expensive than the Aqara and had fractionally slower response times; it also doesn’t work with HomeKit.

Contact sensors, also called door and window sensors, have two parts: a sensor and a magnet. Each part attaches to either side of a door, window, cabinet, drawer—or almost anything else that opens and closes—and when the contact between the sensor and magnet breaks (or gets reestablished), a trigger occurs. That can be as simple as sending an alert to let you know that a door opened, or it can be more complex, like telling your HVAC system to turn off whenever you open the windows (and back on when you close them).

Although you’re likely to use contact sensors mainly on doors and windows, they have lots of creative potential. Place them on curtains, baby gates, fridges, drawers, medicine or liquor cabinets, pet doors, garage doors—anything you might want to know is being opened, left open, or accessed.

This tiny contact sensor is far smaller and cheaper than a lot of other models and works reliably, but it does require the use of an Aqara Hub.

The Aqara Door and Window Sensor is the smallest contact sensor we tested, as well as the cheapest, and we found it easy to mount unobtrusively on a drawer or a door. It works with Alexa and HomeKit or on its own with the Aqara app. In our testing, it was very responsive, turning on a smart bulb in a closet in less than a second, then off again when we closed the door. The Aqara communicates using Zigbee wireless signals and has excellent range, but you’ll also need to purchase an Aqara hub, though that is able to support up to 128 sensors. In our tests it worked perfectly even when sequestered in the top floor of our house at the absolute farthest point away from its hub, and uses an inexpensive CR1632 coin battery.

As with all Aqara sensors, the door and window sensor requires a hub to work, which adds cost to the initial price and complication to the setup. You can’t pair directly to Alexa, like you can with some of the other sensors we tested. You instead have to use the Aqara app, pair the sensor to the hub, and then pair the hub to your ecosystem of choice. You can pair directly to HomeKit by scanning the HomeKit code on the hub and then the sensor.

Slightly larger and more expensive than our pick, but compatible with SmartThings as well as Alexa, this sensor works with Zigbee speakers (like the latest Echo) and works reliably with excellent range.

Compatibility: Amazon Alexa (Zigbee-enabled speakers only), Samsung SmartThings, Zibgee hubs

If you don’t want to use a separate hub or are looking for a SmartThings-compatible device, the Centralite Micro Door Sensor is also inexpensive and small (although bigger than the Aqara sensor). In our tests it had an excellent response time and good range. It has to be paired with a compatible Amazon Echo or Zigbee hub for connectivity and will need that device’s app for setup and configuration.

With a temperature sensor, changes in temperature and humidity in a specific area can trigger a thermostat to adjust, a smart fan or heater to turn on, or smart blinds to lower or raise. That makes them a solution for fine-tuning climate control systems in homes that have only one centrally located thermostat. Temperature sensors are also great for closely monitoring a sensitive space, like a baby’s room, a wine cellar, or an artist’s studio. Some motion and contact sensors have temperature sensors built in, too, so depending on where you want to measure temperature, you might not have to buy a separate device.

This Zigbee sensor works with SmartThings and Alexa without needing a separate hub, has a clean unobtrusive design, and is easy to mount securely.

Compatibility: Amazon Alexa (Zigbee-enabled speakers only), Samsung SmartThings, Zigbee hubs

The Centralite Temperature and Humidity Sensor is an inexpensive, reliable device that has three mounting options (including an option to mount it with screws as opposed to the double-sided tape most sensors rely on), making it easy to install securely. To use it you have to pair directly to a Zigbee-based smart-home hub, such as SmartThings or some Amazon Echo devices, and from there you can set up Automations.

During testing it worked consistently in an Automation we created in both Alexa and SmartThings to lower a set of smart shades in a dining room any time the temperature climbed above 78 degrees. It uses a standard CR2450 coin cell battery that we haven’t had to replace in more than two years of testing.

The only temperature sensor we tested that’s weatherproof, the Eve Weather has an e-ink display that shows the temp and humidity; it’s also Thread-enabled.

May be out of stock

If you want a physical display to see the temperature and humidity at a glance, or want a HomeKit compatible sensor, the Eve Weather is a great choice. It is much more expensive than competing models, but it is the most functional temperature sensor we tested. This is one of the few Thread sensors around, which, if you have a Thread hub, means it can dramatically improve wireless range (see FAQs for an explanation of Thread).

Unlike most other sensors, this one has a visual, e-ink display, so you don’t need to consult your phone to check the temperature; it’s also completely weatherproof, so it can be installed in any location to relay temperature, humidity, and barometric pressure statistics (on its display, in the Eve app, or by asking Siri).

We set up an Automation using the Eve app (HomeKit’s Home app doesn’t allow you to use temperature as a trigger yet) that turned on a smart-plug–enabled fan in a screened-in porch whenever the temp rose above 80 degrees during the daytime. It worked reliably and consistently—in large part because of its Thread connection (in earlier testing of the Eve Degree, this device’s predecessor, we had trouble maintaining a reliable connection over Bluetooth out on the porch).

If you already own a Hue Hub and smart bulbs, you might want to consider the $40 Philips Hue Motion Sensor. The company also has an outdoor motion sensor with the same capabilities. With a Hue hub it also works with HomeKit and can trigger any HomeKit accessory, but the light automations that you activate through the Hue app are much easier to set up than HomeKit’s. Without a hub you can pair the motion sensor directly to a Zigbee-enabled Echo device, and it can trigger any connected accessories. In our testing it was super responsive and consistent, with an excellent range (while using a hub) and amazing battery life (over three years). However, it is much larger than our top pick, the Aqara, and twice the price.

If you’re invested in HomeKit and have a HomePod Mini or Apple TV 4K (2021), consider the Eve Door & Window contact sensor. It’s twice as expensive as our pick, but you don’t need to buy a separate hub. It is also as responsive as our pick. However, it’s larger and chunkier and uses a non-standard expensive battery, and its included stackers to position the magnet correctly look a bit silly.

For kitchens, bathrooms, and covered entryways and porches, consider the Eve Motion Sensor. It may work for some HomeKit homes, and because it’s IPX3 water resistant, it’s a solid choice for potentially wetter spaces. However, it is not Thread-enabled yet, so it relies on Bluetooth. It’s also very big, making it hard to find a discrete spot for it. It does fit well on a shelf or other flat surface and can mount to the wall with a screw, it also uses two AA batteries, which lasted more than two years in testing.

If you need a sensor to work with a Z-Wave thermostat or sun-blocking smart blinds, consider the Aeotec Multisensor 6. It’s a 6-in-1 Z-Wave sensor that monitors light, motion, humidity, UV, and vibration. Its versatile design means you can mount it in the ceiling, power it with a battery or a USB cable and an AC adapter, place it on a flat surface, or use one of two mounting options, but you pay a lot for all these functions and features. Also, in our testing with SmartThings the reaction time was very slow—6 to 8 seconds. The Aeotec TriSensor is a less expensive option if you just want light, motion, and temperature monitoring and don’t need the ability to plug into power (it’s battery only). But it uses an expensive CR123A battery and had just as slow a response time in our testing.

Aeotec will release a SmartThings Multipurpose Sensor and SmartThings Motion Sensor—previously they had been picks and were discontinued by Samsung (Aeotec will also release a SmartThings-certified hub). We loved these Zigbee-based sensors for their ease of use, low price, and ability to pair directly with Zigbee-enabled Echo devices. We will test them when they are available.

In our most recent testing we found that any sensor connected through SmartThings had significantly slower response times than those connected through Alexa or HomeKit. It seems changes to the SmartThings platform are causing this delay. We plan to retest previous sensor picks from Aeotec and Fibaro, along with other Z-Wave and Zigbee sensors when the new Aeotec SmartThings hub is available, as well as with a different Z-Wave hub. In the meantime, if you have a Z-Wave–based smart home we recommend considering sensors from these companies as they worked well in previous testing.

Wyze is releasing version two of its Wyze Sense sensors later this year. Currently, the motion and contact sensors are available as part of the Wyze Home Monitoring security system, which uses the Wyze Sense Hub and works with Alexa. But you have to subscribe to the annual professional monitoring plan for them to work. Wyze tells us that it plans to release them without a subscription as a successor to the original Wyze Sense line, although there is no release date yet.

The $25 Aqara Motion Sensor P1 is now available. Aqara says it will support Thread wireless, and has a battery life of up to 5 years. We plan to test it and will update this guide with the results.

Aqara has also announced a new Door and Window Sensor. Slated to arrive in the second half of 2022, it will support Thread wireless, has an anti-tamper feature, and allows you to adjust the sensitivity using the app.

TP-Link has announced new sensors at CES 2022, as part of its Tapo smart home line: the Tapo T100 Smart Motion Sensor, the Tapo T110 Smart Door/Window Sensor, and the TP-Link Tapo H100 Smart Hub. The hub can act as a siren when triggered by the sensors, both of which feature intruder alerts and options for push notifications. The hub can support up to 64 devices, and includes 19 ringtones and a 90dB adjustable siren.

Newer Echo Show devices have the ability to detect motion using the built-in camera, which in theory can be used to turn on other smart-home devices in a room, such as lights, when you enter. In early testing we haven’t found this to be a substitute for a dedicated motion sensor, as it is quite slow and you have to pass directly in front of the camera, but we will update this guide as we continue to test this feature.

Other sensors we are testing for the next update of this guide include the C By GE Motion Sensor, the Lutron Caseta Motion Sensor, and the Vocolinc Contact Sensor (HomeKit only).

Apple has announced two versions of the Apple TV 4K: a $129 model that is WiFi only, and a $149 that has a gigabit ethernet port. Both can act as a HomeKit hub, however the more expensive model also supports Thread mesh networking, which may be attractive to some smart home owners. We hope to test them soon.

The Fibaro Door/Window Sensor 2 (Z-Wave or HomeKit) is available in multiple colors, making it a good option if you have a variety of decor to fit in with. However, they are expensive and if you need more than one, we think cheaper models are a better option. Also the HomeKit version is Bluetooth not Thread.

The EcoLink Door/Window Sensor Z-wave Plus also provides a brown option, though we found it larger and less attractive than the Fibaro sensor. It installs with tape or screws/brackets for long-term stability and durability and claims an impressive 3-year battery life, but it’s much larger and more expensive than our pick.

The Aeotec Triangle Door/Window Sensor 6 (Z-Wave) gets full marks for ingenuity. This triangle-shaped sensor is as thin as a piece of cardboard and fits snugly in the upper corner of a door, making it very unobtrusive. However, its accompanying magnet is black and stands out unattractively on a white or light-colored door. It also has to be removed and charged every six months, which is annoying.

Aqara’s Temperature and Humidity Sensor works with Alexa and HomeKit but you cannot use it to trigger Alexa routines. HomeKit also doesn’t allow temperature as a trigger so you have to use a third-party app to get any use out of this device, unless you use it just with the Aqara app. It does require an Aqara hub.

The fourth generation Echo smart speaker has a temperature sensor built in, as do Echo Show displays and Echo Plus speakers. These can be used to trigger Alexa routines when the temperature in a room reaches a set point. This is useful if you have smart shades in a room where your speaker is or want to trigger a smart thermostat to adjust or a fan to turn on if a room gets too hot. However, we wouldn't recommend purchasing a smart speaker just for this function. One of our picks is less expensive and can be more easily placed in a convenient location to measure temperature.

There were a number of devices we considered but didn’t test because they didn’t meet one or more of our requirements, were overly large with a dated design, or had lots of poor customer reviews for things like battery life or customer service complaints. There were also sensors that performed poorly in our tests, including the following.

The Echo Flex is an Alexa speaker that plugs directly into an outlet. There are compatible motion sensors you attach to the base using a USB port. In our testing we found this to be unreliable at triggering Alexa Routines, sometimes taking several seconds to react and sometimes not working at all. Also, because it has to be plugged into an outlet it can be difficult to adjust the angle. The most useful place for this is in a hallway to turn on lights as you walk past, but as most outlets are in the middle of the hall rather than at the beginning, you’ll be walking in darkness most of the way.

The Onvis Motion Sensor is a motion sensor that also measures temperature and humidity. At under $25 it is the least expensive HomeKit-compatible motion sensor available without a hub, and because it’s a Bluetooth 5.0 device it responds really quickly, even at a distance. But it was not reliable in our testing, we had to reconnect it multiple times, and its app verges on useless. It is also very large and doesn’t work with Alexa or SmartThings.

The Ecolink Z-Wave PET Immune Plus Motion Detector is large and has a fixed four-to-five-minute reset time, which really only makes it suitable as a security device since it will ignore you for large chunks of time after triggering once. It has a great battery life and a 45-foot range, but its touted pet immunity failed in our testing.

The Ecolink PET Immune Motion Detector Zigbee is large, hard to mount, and rarely if ever worked to trigger routines through Alexa, which it pairs to directly without a hub.

The Ecolink Door/Window Contact Zigbee Sensor has a completely different design from the Z-Wave version and only comes in white but is slimmer and sleeker. It pairs directly with a Zigbee-enabled hub, including Echo speakers, and when we first tested it it worked reliably. But it unpaired itself from the Echo at some point, and we could never get it to reconnect.

The Monoprice Stitch Door and Window Sensor is the only contact sensor that connects to Alexa through Wi-Fi and is capable of triggering Routines. It can connect directly with any Echo, not just the Zigbee-enabled ones. It’s inexpensive and attractive, but it’s comparatively bulky because it uses two AAA batteries to keep running on power-sucking Wi-Fi. Additionally, in our testing it took between two and eight-plus seconds to trigger a Routine—much longer than sensors that connect via Zigbee. Also, Monoprice’s native app has a truly heinous-sounding alert on your smartphone, which you cannot change (although you can turn it off, which we did immediately).

Setting up sensors with Alexa is very simple. You just need a Zigbee-enabled Echo: either the Echo 4th Gen, Echo Studio, Echo Plus, or Echo Show. Activate the sensor following the manufacturer instructions and Alexa will discover it. Then you can link the sensor to your other Alexa-compatible devices with Routines. So, instead of having to ask Alexa to turn on the lights when you enter a certain room, they’ll just turn on automatically when you walk in. This article explores different ways to use Routines.

The downside of using sensors with Alexa is that the Alexa app offers no direct access to a sensor’s controls, so you can’t adjust motion sensitivity, nor can you find logs of the temperature over a time period or of activities, such as when a door is accessed. These features are standard in competing smart-home ecosystems such as SmartThings and HomeKit.

SmartThings is compatible with a wide range of Z-Wave and Zigbee sensors (see a list here). To pair a sensor with a SmartThings-certified hub, first check if it’s compatible, select “Add a device” in your SmartThings app, follow the steps to include it in your network, and then install it and check that it’s responding correctly. Initially, devices may need to be closer to the hub, but the more devices you add, the farther your network will extend, as both Zigbee and Z-Wave devices can act as repeaters, creating what’s called a mesh network in your home—each device ensures other devices stay online. Choose from pre-set automations such as Smart Lighting, which uses motion sensors to activate smart lighting, or create custom automations using “if then” commands: If this sensor detects something, then make this happen.

To pair your sensors with HomeKit, you’ll need an iPhone updated to iOS 10 or later, or a Mac running Mojave or later, and a HomePod, HomePod Mini, Apple TV (tvOS 11 or later), or an iPad (iOS 11 or later) to act as a home hub (for more details, see the full list of requirements). Although you technically don’t need a hub to use HomeKit devices, you do need one if you want to use Automations and have them continue to work when you’re not at home. (For more info on how to set up devices with HomeKit, check out “How to Build an Apple-Based Smart Home System With the Best HomeKit Devices.”)

Once you’ve set up sensors in your home, you can use the Home app (preinstalled on all iPhones and iPads) to create Scenes and Automations that then use those sensors to tell your home how to react to motion and activity (HomeKit doesn’t offer temperature as a trigger but you can use a free third-party app, such as the one from Eve to set this up). You can also tailor those actions to the time of day and who is at home. For example, you might have the shades lower only if it’s after sunset, or you might personalize which lights turn on based on who arrives home and when (which your HomeKit system detects based on the presence of their smartphone). The person-specific trigger is a great aspect of HomeKit, one that most other hubs don’t offer, and it makes sensors much more useful in multiperson homes.

Yes and no. Some sensors, including our Aqara picks, can be added to your Google Home app and queried with voice: “Hey Google is my front door open?” But for now, that’s the only way to interact with sensors using the Google Home platform. You can’t ask about temperature or motion, or access any of that information in the Google Home app. And you also aren’t able to trigger Google Assistant Routines.

There are several Google Home-compatible sensors, including Z-Wave and Zigbee sensors from Aeotec and Fibaro (paired through a SmartThings hub), and those you can pair through security systems—Abode and Simplisafe for example. But no third-party sensor has any functionality with Google Home beyond voice queries.

Recently, Google introduced presence sensing to the Google Home app. This mimics some of the functionality you can get from a motion- or contact-sensor-based automation. Using sensors in some Google Nest products (including the new Nest Thermostat, the wired Nest Protect smoke alarm, and the Nest X Yale Lock) combined with your phone’s location, you can set up a routine to activate smart lights, plugs, switches, cameras and thermostat. But this is limited only to leaving or arriving so you can’t have lights turn on just when you enter a room or any of the other useful things smart sensors can do while you’re in the house.

A new(ish) smart-home protocol that should make devices like smart sensors work faster and more reliably. Similar to Zigbee and Z-Wave wireless, Thread is a wireless system that enables devices to share signals with each other, but unlike those systems Thread devices will connect directly to the internet, though you’ll still need what’s called a Thread Border Router that lives on your home Wi-Fi network (currently only the HomePod Mini and 2021 Apple TV 4K are available).

So far, the only Thread-compatible sensors are the Eve Door and Window (contact sensor) and Eve Weather (temperature sensor). In our testing, response times compared with the previous Bluetooth versions of these devices were cut in half—almost instantaneous. And the previous range issues we had with both devices were solved. But they were no faster and reached no farther than our top picks from Aqara and Centralite, which work on Zigbee.

We’ll test any new Thread sensors and devices as they become available and will update this guide accordingly.

Sometimes. If you own a smart-home hub such as one from SmartThings, or have a smart home security system from Abode, Honeywell, Ring, or Scout, then yes, their smart sensors may be able to be added to the HomeKit, Alexa, and Google Home apps (check compatibility to ensure before you buy). However, in testing, we found a slightly longer delay in Routines that were triggered by sensors that are also connected to a security system. But if you already have these installed, it’s definitely worth trying them out before spending any more on new sensors.

Crucially, for some uses, contact sensors from security companies often have the ability to trigger a chime when the door opens and closes; both the Ring and Abode sensors have this capability. If you are using Alexa, you can set up a Routine in which Alexa announces a trigger instead, such as “The front door has opened.”

Christian Taubman, director of Alexa Smart Home, phone interview, May 29, 2019

Mitchell Klein, executive director, Z-Wave Alliance, phone interview, February 22, 2019

Paul Lamkin, The best smart home sensors, The Ambient, April 21, 2021

Cees Links, Smart Home Sensors Differ From Other Types, Sensors Mag, January 13, 2017

Christopher Close and Karen S Freeman,, Best HomeKit motion sensors 2021, iMore, June 23, 2021

Jennifer Pattison Tuohy writes about smart-home technology use and sustainable living, while trying to practice both (one is a lot easier than the other).

If you want to make the jump from dull lighting to smart lighting, here are some easy ways to get started.

Anyone who uses an iPhone and is interested in a smart home should start here to find the best options and advice for getting started.

We selected the best smart-home devices to work with your Alexa speaker, based on our extensive testing and real-world use.

by Grant Clauser and Signe Brewster

Amazon Alexa and Google Assistant make listening to radio, controlling smart devices, and creating reminders as simple as asking for it. Here’s how to pick.

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