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Contact sensor
A contact sensor is a two-piece device that detects when a door or window is opened or closed by sensing the separation of its halves.
Why it matters
Contact sensors are the backbone of a security system, triggering alerts when entry points are breached.
Where people get this wrong
A contact sensor does not detect glass breaking or motion. It only knows if the door or window frame has separated.
Real-world example
A contact sensor on the back door sends an alert to your phone when someone opens it while the system is armed.
Where this hits your build
This matters during rough-in and before drywall. Once walls close, adding or moving wiring becomes expensive. Plan ahead.
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