They are one of cheapest, simplest and at the same time very efficient detection devices. Magnetic contact is composed out of two separate elements; magnet and contact. After dilation of both of elements alarm circuit is either closed or opened - it depends on magnetic contacts work mode NC (normally closed) or NO (normally opened). Those devices are ideal for signalization of door and window state (open/close). Wide variety of construction solutions allows using them in any alarm system. Magnetic contacts are being used also in access control systems where they inform about state of doorway.