You already know the door is the thing you cannot watch all night. A door contact alert is a small pair of parts, one on the door and one on the frame, that tells you when the door opens. The install takes less time than the planning. The parts that go wrong are the gap, the chime that never reaches the room where you sleep, and the battery nobody owns. This piece walks the install from the first question to the final test, then names who checks it each month.
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Decide who hears it before you buy anything
Write down the person or people who must hear the alert. Often that is you in another room, a caregiver on a shift, or a neighbor with a key. Some kits ring a chime in the house only. Others send a message to a phone. Compare them on three things: whether the receiver sits where the sleeping person can hear it, whether the alert can reach a phone when you need it there, and whether any ongoing fee applies. Check the fee line on the box or product page before you open the package.
Check the door and the frame
Stand at the door and look at three things. First, which side moves. The magnet or sensor goes on the moving slab, and the other part goes on the frame or jamb. Second, whether there is solid wood on both sides where the parts will sit, because loose trim that pulls away will fail. Third, whether the door seals tightly when closed, since rubber weatherstripping can compress and change the gap over time. If the door is fire-rated or part of a building's required exit path, ask the building owner or a qualified installer before you drill.
Read the gap rule on the package
Every kit lists a maximum distance between the two halves when the door is closed. Find that number and write it down. Then measure the actual gap at the spot you plan to mount, with the door closed and latched the way you normally latch it. If the gap is larger than the package allows, the sensor will report open all the time or not at all. Do not guess. Measure at the top, middle, and bottom of the door, because a door that sags opens a wider gap at one end.
Mount it in order
Dry fit first. Close the door and hold the magnet on the door and the sensor on the frame, with the alignment marks matched. Mark the screw holes or adhesive spot with a pencil. Clean both surfaces with a dry cloth. If you use adhesive, follow the cure time on the label before you test. If you use screws, drive them into solid frame wood behind the trim, and drill a pilot hole if the wood is hardwood or the screw is thick. Mount the magnet so it sits flush with the door edge, and mount the sensor directly opposite on the frame, with both halves on the same plane.
Power it and pair it
Insert the batteries in the sensor and the receiver. Pair them following the printed steps. Most kits show a light or make a short sound when paired. Write down how the pairing confirmation looks so you can recognize a failed pairing later. Then open and close the door slowly and watch the indicator change.
Test the gap and the reach
Close the door and confirm the indicator shows closed. Open the door a few inches and confirm the alert fires. Then test the real route. Stand in the room where the receiver's chime should be heard, at the volume it will run at night, and open the door. If you cannot hear it from the bed, move the receiver, add a second chime if the kit allows it, or switch to a phone alert. Test from the place the caregiver usually stands too. Close the door firmly, not gently, and repeat the test to see whether the mount holds.
Name the owners
An alert that works today can stop working when a battery dies or a screw loosens. Write three names: who checks the alert and the indicator, who replaces the batteries, and who gets called when the alert stops responding. If you are the only name on the list, the plan fails the first week you are unavailable. Ask a second person to hold one of the roles, even if that person only checks on a set day each week.
Run the monthly check
Once a month, open and close the door and confirm the chime or phone alert. Check the magnet and sensor for loosening, paint buildup, or swelling wood. Look at the battery indicator if the kit has one, and replace batteries on the schedule the package lists rather than waiting for a chirp. If the alert fires when no one opened the door, check for a door that has sagged, a mount that has shifted, or a magnet that has moved away from the sensor. Keep the check on the same calendar line as your other household checks so it does not depend on memory.
Permission
You do not have to be the only person who hears the door at night. Putting this alert in place means someone is named to hear it, and that someone can be you on a phone in another room. Finish the test, write the three names, and stop for the night.