Passive infra-red sensor, add this unit to your home automation system to add greater flexibility. String together some automation rules to control your devices when the pir is triggered ie, turn on your security lights, turn on the hallway light but only between specified hours, start recording your camera. This device will push notifications to your smart device to alert you to intruders? Installs to the same app, is only golf ball in size add rechargeable batteries (cr123a 3v not supplied) or use the inbuilt usb port.