By requiring that both systems detect an intruder before an alarm is activated, a high degree of reliability can be obtained. Perimeter ... A permanent magnet is mounted on the movable component of a door, a window, or some other access opening. A reed ... alarm. If the door is attacked and an attempt made to disable the switch, the flux density may decrease to a level below the lower limit of that range.
|Title||:||Handbook of utilities and services for buildings|
|Author||:||Cyril M. Harris|
|Publisher||:||McGraw-Hill Companies - 1990-04-01|