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A simple electromagnetic door holder consists of a strong electromagnet, usually attached to a wall or mounted in a floor pedestal enclosure, next to the door it controls. The mechanism may be mounted near the floor, at the upper corner of the open door, or at any convenient height along the latch edge (away from the hinged edge).
These vary in effectiveness, usually failing from high false positive alarms, poor database configuration, or lack of active intrusion monitoring. Most newer access control systems incorporate some type of door prop alarm to inform system administrators of a door left open longer than a specified length of time. [16] [17] [18]
These door holders were traditionally used to hold doors open, but in this application Saphirstein believed that they could be packaged and adapted to work as a fail-safe lock. After a successful prototype and installation at the Forum, Saphirstein continued evolving and improving the design and established the Locknetics company to develop ...
Examples are door and window sensors in burglar alarm systems and tamperproofing methods. Reed switches have been used in laptops to put the laptop into sleep/hibernation mode when the lid is closed. Speed sensors on bicycle wheels frequently use a reed switch to actuate briefly each time a magnet on the wheel passes the sensor.
Some have alarms activated when they are opened, to alert staff of unauthorized use during non-emergencies. [8] On many exits, the user may have to push against a crash bar or other door opening device for a period of time to unlock the door. Many exits have a sign reading, "Emergency exit only, alarm will sound if opened", to warn of the fact ...
The back door to the house was reportedly kicked in and a safe left open. Yet the alarm system did not trigger and the cameras were down. No one was in the residence at the time of the break-in ...