Doors/Windows

Contacts on perimeter doors and windows, and other movable openings, provide a first line of defense and early warning against intrusion.  Door and window contacts may be either hardwired or used with a wireless transmitter.  They may be recessed into the door or window and its frame, or they may be surface mounted.   Because recessed contacts are hidden, they are more secure and usually preferred.

There are two types of contacts, magnetic and mechanical:

Magnetic contacts have two parts, the magnet which is attached to a door or window, and an electrical switch attached to the frame.  When the door or window is closed, the magnetic force closes the switch and completes the electrical circuit.  When the door is opened, the circuit is broken, which activates the alarm.  (Note that glass in the window or door can be broken without disturbing the contacts themselves.  This means other protection is necessary to completely protect these points of entry.)

Mechanical contacts operate in the same manner, except, instead of using a magnetic force to open and close contacts, a physical force is used.  Contacts are enclosed in a plastic housing and are generally trouble free.  However, loose fitting doors or windows could cause the contacts to separate creating a false alarm.  (Note that glass in the window or door can be broken without disturbing the contacts themselves.  This means other protection is necessary to completely protect these points of entry.)

Glass-Break Protection

Sound discriminators, or glass-break detectors, provide economical area detection of breaking glass for perimeter protection.  Sound discriminators are placed on interior walls and ceilings as perimeter protection for large areas of windows and glass doors.

A sound discriminator is an adjustable sensitivity microphone that senses the sharp sounds of breaking glass.  Even though sound discriminators react to breaking glass, some discretion should be made when applying this protection in environments where heavy machinery is used, close to railroad tracks, fire stations, or under airport flight patterns, due to sounds generated in these areas.

Security Screens

Security screens are detection devices which provide perimeter protection while allowing for ventilation.  Security screens are typically used on windows that are going to be opened for ventilation and on other openings, such as skylights, where normal contacts can't be used effectively.

This form of detection device is constructed by interlacing wire through a screen.  A contact is also fitted to the screen and window frame.  Any attempt to cut or rip the screen breaks the interlaced wire and activates the alarm.  Screens can be custom made to fit any opening.