The Entry sensor comes in 2 parts: the small magnet, and the larger transmitter.
When the magnet is far away from the transmitter, the sensor reports "Open". When the magnet is close to the transmitter, it reports "Closed".
It doesn't matter if you put the magnet on the door and transmitter on a door frame, or the magnet on the door frame and the transmitter on the door. The only thing that matters is that you align the arrows pointing toward each other, and keep the gap between the magnet and transmitter smaller than about 0.5" / 12 mm.
- Peel off the sticky backing from the magnet and the transmitter.
- Stick the magnet to the door or window frame, stick the transmitter to the door or window (or vice versa).
- Inside the Presence app, test to make sure the entry sensor reports "closed" when the door or window is closed, and "open" when the door or window is open. You may need to refresh your list of devices to get a faster update, or tap into the sensor's user interface.
It's possible to install the magnet at an angle (even rotated 90 degrees!), but always test it in the app to make sure it's working as you expect.
The Entry Sensor will automatically alert you when its battery is getting low. It takes a CR2032 Lithium coin cell battery, which should last a few years.