Onvis Alarm Sensor CS2

The Onvis Alarm Sensor CS2 is a door and window contact sensor with a siren built in. Most contact sensors only report the state of the door and rely on something else to make a noise. This one sounds its own alarm at the door, which is a different job: it is what makes an opportunist step back off a garden gate or a shed.

It also carries a thermometer and a hygrometer, so it doubles as a room sensor when the door is shut.

What works in Apple Home

• Report the door or window as open or closed.
• Report temperature and humidity as separate accessories.
• Trigger scenes and automations, and be read by Siri.
• Report its own battery level.

Connectivity

Thread is the reason to prefer this over an older Bluetooth sensor. Bluetooth accessories talk to one hub and get slower and less reliable the further away they sit. Thread accessories form a mesh, where every mains-powered Thread device passes messages along, so a sensor at the far end of the house responds as quickly as one in the hall.

You need a Thread border router for it: a HomePod mini, a HomePod (2nd generation) or an Apple TV 4K.

Before you buy

Contact sensors depend on the gap between the two halves. Check the alignment of your door or window frame, because a warped frame or a deep rebate can hold the magnet too far from the sensor for it to read reliably.

If you want the sensing without the siren, Onvis sells simpler contact sensors, and a plain contact sensor is usually cheaper per door if you are fitting several.

Specifications