Motion sensors
A smart motion sensor tells the house someone has walked in, so a light, fan or heater responds without anyone touching a switch. A presence sensor also registers someone sitting still, so the lights stay on while you read.
Motion or presence
A motion sensor such as the BLU Motion uses passive infrared and reacts to warmth moving across its view, then goes quiet once you stop moving. A presence sensor uses mmWave radar. The Shelly Presence Gen4 registers a person who isn't moving within 3 m.
Battery or plugged in
Motion sensors sleep between movements, so they last years on batteries: up to five years on the BLU Motion's coin cell, and two AAs or AAAs in the Hue sensors. Radar never stops watching, so a presence sensor needs constant power from a USB-C adapter.
What it reports to
The Hue sensors need the Hue Bridge. The BLU Motion talks Bluetooth to a mains-powered Shelly, which acts as its gateway. The Presence Gen4 joins your Wi-Fi with no hub.
Light, not just movement
Every sensor here also measures light. An automation can ignore movement in a room that's already bright, so the hallway light only comes on after dark.
Sensors · 4 products Motion Sensors at Synced Australian stock
Filter guide
Which protocol should I pick?
Protocols are the wireless languages smart devices use to talk to each other. Some need a hub, some run straight off your Wi-Fi. Here's what each one means for your setup.
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Zigbee
Low-power meshThe cleanest mesh for a bigger setup. Every mains-powered device repeats the signal, so coverage grows as you add more. Needs a hub like a Hue Bridge or SmartThings.
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Wi-Fi
No hub neededThe simplest way to start. Plugs into your existing Wi-Fi with no extra hardware. Best for a handful of devices; very large setups can crowd the network.
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Bluetooth
Direct, short-rangeGood for setup and close-range control from your phone. Range is short with no remote access on its own, so it's often paired with a hub or bridge.
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Compatibility guide
Which platforms does it work with?
Works with shows the smart home platforms a device pairs with, so you can control it from the app and voice assistant you already have. Here's what each one is.
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Apple Home
Apple ecosystemPairs with Apple Home, so you control it from the Home app and Siri across your Apple devices. Look for this if your household runs on iPhones.
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Google Home
Google ecosystemWorks with the Google Home app and Google Assistant, for voice control through Nest speakers and displays or your Android phone.
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Amazon Alexa
Alexa voicePairs with Amazon Alexa, so you can control it by voice through any Echo speaker or display and the Alexa app.
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Samsung SmartThings
SmartThings hubWorks with Samsung SmartThings, controlled from the SmartThings app. Handy if you've already built your setup around Samsung phones or appliances.
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Home Assistant
Open-source hubWorks with Home Assistant, the open-source platform for people who want full local control and custom automations. More hands-on, very flexible.
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Power guide
How is it powered?
Battery-powered devices go anywhere. Anything that needs a cable has to sit within reach of a power point.
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USB
Needs a power pointPowered over a USB cable from a plug-in adapter. Nothing to recharge or replace, but it needs a power point within reach of where it mounts.
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Battery
No wiringRuns on its own batteries, so it mounts anywhere without a cable or a power point. You change the battery every year or more, depending on the model.
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Battery guide
Which battery does it take?
Most sensors run for a year or more before the battery needs changing. The size decides where you can buy a spare.
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CR2477
Large coin cellA thick lithium coin cell, much larger than the thin coin cells in a car remote. The extra size is what lets a sensor run for years on one.
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AA
Standard sizeThe standard cylindrical battery, and the easiest size to find a spare for.
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AAA
Slim sizeThe slimmer cylindrical battery, used where a sensor needs to stay small. Just as easy to find as AA.
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Sensing guide
Motion or presence?
A motion sensor sees you move. A presence sensor also sees you stay, so the lights don't drop out while you sit still.
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PIR
Sees movementPassive infrared: it reacts to warmth moving across its view, which is quick and light on battery. Once you sit still it has nothing to see, so it reports the room as empty.
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mmWave radar
Sees you sitting stillMillimetre-wave radar picks up much smaller movement than infrared, so it keeps registering someone at a desk or on the couch. It is always on, so it needs constant power rather than batteries.
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Buying guide · Motion sensors
What is the difference between a motion and a presence sensor?
One sees you move. The other sees you stay.
A motion sensor watches for warmth moving across its view. Walk into the room and it reports motion within a moment, which suits anywhere people pass through. Sit down and stop moving, and it has nothing left to see. After the delay you set, it reports the room as empty and the lights go off.
A presence sensor uses mmWave radar instead. Radar picks up much smaller movement than infrared, so it keeps registering someone at a desk or on the couch. The Shelly Presence Gen4 does this within 3 m and can split a room into up to 10 zones, so the reading lamp can follow the armchair while the ceiling light follows the doorway.
The trade-off is power. Radar is always on, so a presence sensor runs from a USB-C adapter rather than batteries, and it needs a power point within reach of where it mounts.
What does each sensor report to?
A sensor is only useful once it reaches something that can act on it.
The Hue Bridge
Zigbee Both Hue sensors join the Bridge, and the motion rules live there, so the light comes on whether or not your phone is home.
A Shelly gateway Check before buying
Bluetooth The BLU Motion broadcasts over Bluetooth to a mains-powered Shelly that has its Bluetooth gateway switched on. Without one in range the app can't hear it.
Sensors 
Shelly BLU Motion
Shelly BLU Motion Your Wi-Fi, directly
Wi-Fi 
Matter Zigbee The Presence Gen4 ships with Matter over Wi-Fi and needs no hub. Five presses of its button swap it to Zigbee firmware if you'd rather run it from a Zigbee coordinator.
Sensors 
Shelly Presence Gen4
Shelly Presence Gen4 Frequently asked questions
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What you can do with them
Lights that come on as you walk in, softer late at night
A sensor turns the bedroom or hallway light on as you walk in, at full brightness in the evening and a low glow at 2am. Fit Philips Hue bulbs and a motion sensor, or keep your lights and add a Shelly dimmer and presence sensor. Control with any of
Outdoor lights on at sunset, off at midnight
Porch, path and garden lights follow the sun through the year without you touching a switch. Run the lights you have from a Shelly relay, or fit Philips Hue outdoor lights, and set it up in their app or Home Assistant. Control with any of