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2. Electromagnetic door holder - Wikipedia

   en.wikipedia.org/wiki/Electromagnetic_door_holder

   An electric current typically energizes the electromagnet to attract and hold the steel plate, keeping the door open. Unlike electromagnetic locks, the magnetic attraction of an electromagnetic door holder is usually weak enough that it can be manually overpowered at any time by anyone, allowing the door to close. [citation needed]

3. Reed switch - Wikipedia

   en.wikipedia.org/wiki/Reed_switch

   Reed switches actuated by magnets are commonly used in mechanical systems as proximity sensors. 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.

4. Security alarm - Wikipedia

   en.wikipedia.org/wiki/Security_alarm

   Wireless home alarm system control panel A house alarm. A security alarm is a system designed to detect ... Installing a wireless magnetic contact breaker on a door.

5. Electromagnetic lock - Wikipedia

   en.wikipedia.org/wiki/Electromagnetic_lock

   Fail-safe locking devices are unlocked when de-energized. Direct pull electromagnetic locks are inherently fail-safe. Typically the electromagnet portion of the lock is attached to the door frame and a mating armature plate is attached to the door. The two components are in contact when the door is closed.

6. Electronic lock - Wikipedia

   en.wikipedia.org/wiki/Electronic_lock

   The most basic type of electronic lock is a magnetic lock (informally called a "mag lock"). A large electro-magnet is mounted on the door frame and a corresponding armature is mounted on the door. When the magnet is powered and the door is closed, the armature is held fast to the magnet. Mag locks are simple to install and are very attack ...

7. Fire alarm system - Wikipedia

   en.wikipedia.org/wiki/Fire_alarm_system

   A fire alarm system is a building system ... Magnetic smoke door holders and retainers are wall-mounted solenoids or electromagnets ... Contact Wikipedia;