Door sensor is a set of a magnet and corresponding switch that is installed in the door jamb and the door respectively. These are included with your purchase of the Gainsborough Freestyle Wi-Fi Bridge, and are positioned above the latch and the strike plate.
The magnet engage or disengage the switch when the door is in use. And the app can tell you whether you’ve shut your door or left it ajar.
This is especially useful when used along with a Wi-Fi Bridge. You can see the door status as well as your lock status from anywhere through the Freestyle app.