How does the Recessed door sensor tell if the door is open or closed? Follow The Recessed Door Sensor works like a regular door sensor and can tell when the door is open when the two pieces (Transmitter and Magnet) are within ¾” of each other. When they are apart from each other, the sensor will report open. Facebook Twitter LinkedIn Comments 0 comments Article is closed for comments. Articles in this section What do I do if my Recessed Door Sensor status say offline or malfunction? How is the Recessed Door Sensor armed? How do I make sure my Recessed Door Sensor is working properly? What is the temperature range my Recessed Door Sensor can operate in? Are there types of doors my Recessed Door Sensor is not compatible with? How does the Recessed door sensor tell if the door is open or closed? How do I mount the Recessed Door Sensor?