The Doorway
The Door Alert Tells You It Opened: Compare Chimes, Contact Sensors, Pressure Mats, and Doorbell Cameras
Each kind of door alert tells you something different, so the right one depends on which doors she tries and whether you need to know the door moved or that she has stepped through it.
A door alert tells you that something happened at a door. The common types do not all tell you the same thing, and choosing the wrong one means you hear about the door after she has already been through it. Compare the four common types by what each one detects, how it reaches you, and what it asks of the house.
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What each type detects
A magnetic contact sensor sits on the door and the frame. It senses when the door opens or pulls away from the frame, so it works on any door that actually opens and shuts. A chime is usually paired with a sensor or a plug-in receiver and sounds in the house when the door opens. A pressure mat sits on the floor in front of a door or along a hallway and senses weight, not the door itself, so it tells you someone has stepped onto it. A doorbell camera watches the entry and shows who or what has come to the step, often with a video record.
How the alert reaches you
A chime is heard only where the sound carries. Test it from the room where you usually sit and from the bedroom with the door closed. A phone alert needs the sensor linked to a hub or an app, and to a network that stays on. Ask what happens when the internet drops, whether the alert still sounds in the house, and whether more than one phone can receive it. A camera adds a picture, which helps, but it depends on light and on a network too.
What each asks of the house
A contact sensor and a chime are small and usually fit on a door in an afternoon. Check that the magnet lines up when the door closes, and that the sensor does not sit where a storm door or screen door will bump it. A pressure mat is the one most likely to become a trip hazard, so look at where it sits and whether it slides on the floor. Keep it clear of the path a walker or wheelchair takes. A camera needs a mount, power or a battery, and a network connection at the door. Make sure no alert, mat, or cable blocks the way out in an emergency.
Questions to ask before you choose
Ask which doors each type can cover and whether it works on a sliding door. Ask how loud the chime is at the bedroom door at night. Ask how the battery warns you before it runs out, and who replaces it. Ask whether phone alerts carry a monthly fee and what that fee covers. Ask what the alert shows: the time of the opening, or only that it happened. Write the answers down so you can compare the types side by side instead of from memory.
The alert is only a signal. It does not stop a door from opening, and it is most useful when someone has already decided who answers it and what they do next. The Start Here page lays out that order from dusk to morning, and it is worth reading before you buy anything.