Where should I position a recessed contact sensor in a door?
Honestly, there is no right or wrong here. The preferred location is either the top of the door or on the side (either hinges-side or the opposite of). You will want to place the sensor so it is easier for you to wire it to the control panel. For example, if this is the basement door and the control panel is on the top floor; you may want to install the sensor on top of the door so you can directly wire it up.