A door contact, or magnetic reed switch, consists of two small parts — one on the door or window frame and one on the moving door or sash — that maintain a closed circuit while aligned. Separating them, as when the door opens, breaks the circuit and signals the alarm panel that the opening has occurred.
On a real property, contacts are placed on exterior doors, gates, and sometimes interior doors to sensitive rooms like an electrical closet or a leasing office safe. They are simple and reliable but only report open/closed status — they cannot tell whether the person opening the door is authorized.
Failure modes include misalignment after a door settles or is slammed repeatedly, low battery in wireless contacts, and doors intentionally propped in a way that keeps the contact aligned while defeating the door's actual closure. A contact reporting normal does not guarantee the door is actually secured, such as when a latch fails to catch.
In a patrol program, a door contact alert routes to a monitoring center or panel that notifies a patrol officer to verify the door in person, and officers checking doors during rounds provide a manual backup to the sensor's automated report.
Related entries
Official sources
- [1]NIST intrusion detection systems overviewNational Institute of Standards and Technology
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General industry and regulatory usage — not legal advice, and not an endorsement by BSIS, the Department of Consumer Affairs, or any law-enforcement agency. Statutes, regulations, and local ordinances change; verify current text at the official government source or with your attorney.