A genuine five-function Zigbee sensor in a single battery-powered unit. One device reports motion, occupancy, ambient temperature, relative humidity and light level (lux) – each as a separate entity in your hub – instead of needing four or five individual sensors scattered around the room.
Compatible with every major Zigbee 3.0 hub – Home Assistant (Zigbee2MQTT or ZHA), SmartThings, Hubitat, Aqara Hub M2 and any other standards-compliant coordinator. Uses the standard Zigbee clusters for each measurement (Occupancy Sensing, Temperature Measurement, Relative Humidity, Illuminance Measurement), so it works as a generic multi-sensor without any vendor-specific apps or drivers needed.
Five functions in one device
Most smart home sensors do one thing. This one combines five, which is useful for two reasons. First, it cuts down on physical clutter – one unit on the wall instead of three or four. Second, it means automations can correlate signals: “if temperature drops below 18°C AND no motion for 30 minutes, dim the lights and turn the heating up” is a single-sensor automation, not a multi-device dance.
- Motion (PIR) – detects movement events with low latency. Used for lighting, security alerts, and presence-based automations.
- Occupancy – a longer-window “is the room occupied right now” state, separate from individual motion events. Useful for HVAC and lighting that should stay on while people are present.
- Temperature – ambient room temperature, ±0.5°C accuracy. Drives heating automations, hot/cold alerts, and historical climate logging.
- Humidity – relative humidity in percent. Detects damp issues, drives bathroom extractor fans, or triggers humidifier/dehumidifier automations.
- Illuminance (lux) – ambient light level. Enables conditional automations like “only turn on lights when it’s actually dark” rather than firing every time motion is detected in broad daylight.
Unique form factor – wall-socket mountable or freestanding
The sensor ships with a mounting frame that fits the standard UK 86 × 86 mm socket front-plate, meaning you can clip it onto any unused light switch or plug socket position at the perfect height for motion sensing (typically around 1.5 m above floor level). No drilling, no adhesive, no battery management headaches.
Pop it off the frame and it works as a standalone freestanding unit – good for portable use, mounting in unusual places, or moving between rooms to characterise temperature/humidity before installing permanently.
The frame approach is more practical than it sounds. Motion sensors traditionally need to be mounted at human-detection height, which means drilling into walls. Using an existing socket position skips that entirely and gives a clean, professional look.
Hub compatibility
Generic Zigbee 3.0 device using standard clusters. Works with any Zigbee 3.0 coordinator:
- Home Assistant (Zigbee2MQTT or ZHA) – fully local. Recognised as a Samotech SM321 with five separate entities exposed.
- SmartThings – pairs as a generic Zigbee multi-sensor. All five measurements available as separate attributes.
- Hubitat – multi-sensor driver supports all five outputs locally.
- Aqara Hub M2 / G3 – works as a third-party Zigbee device. All measurements available for automations within the Aqara app.
- Amazon Echo Plus / Echo Hub – pairs directly to any Echo with built-in Zigbee for Alexa routines.
- Philips Hue Bridge – paired as a third-party Zigbee 3.0 device. Motion events are exposed; temperature/humidity may or may not depending on bridge firmware version.
For the most flexible setup, Home Assistant with Zigbee2MQTT exposes all five measurements with their full configuration options – occupancy timeout, reporting interval, sensitivity – directly in the device’s settings page.
Battery life
Powered by 2 × AA batteries (alkaline or rechargeable NiMH both work fine). Typical battery life is 18-30 months depending on environment and reporting frequency. Battery level is reported to the hub via standard Zigbee battery reporting, so you get plenty of warning before a change is needed.
Battery life is affected primarily by motion event frequency – a sensor in a busy hallway with constant traffic will report more often than one in a low-use guest bedroom. Reducing the reporting frequency in your Z2M settings for non-critical measurements (e.g. temperature can update every 5 minutes rather than every minute) extends life significantly.
Installation and pairing
Out of the box, insert 2 × AA batteries and the sensor wakes up. With your hub in pairing mode, hold the pairing button for 5 seconds – the indicator LED flashes and the device joins within a few seconds.
Mounting options:
- UK socket front-plate – use the supplied frame to clip onto any unused socket position. Sits flush with the wall plate.
- Adhesive pad – stick directly to any clean, flat surface using the supplied 3M pad.
- Freestanding – sits on a shelf, mantelpiece, or windowsill. Good for portable monitoring or temporary placement.
- Screw mount – two screw holes for permanent installation, screws and wall plugs included.
For best motion detection, mount the sensor 1.5-2.3 metres above floor level, with the PIR lens facing the area to be monitored. The 110° detection angle covers a wide room from a corner position.
Specifications
What’s in the box
- 1 × Zigbee multi-sensor (SM321)
- 1 × UK socket-frame mounting plate
- 1 × 3M adhesive pad
- 2 × Mounting screws and wall plugs
- Quick-start guide
Batteries are not included – any pair of AA alkaline or NiMH rechargeable cells works fine.
Great to have a few more features in the same sensor