Security System Sensors
Sensors So you're wondering what these "sensors" are that I've been talking about. The most common alarm contact is probably a magnetic switch. These are those little rectangular plastic gizmos that you may have seen attached to doors in stores or homes. They consist of a switch which is sensitive to a magnet; when the magnet is near, the switch is closed, completing a circuit, and when the magnet moves away (when the door or window opens), the circuit is broken, causing the alarm to sound. This type of switch is considered "normally closed" or N.C., because in it's normal state (door closed), the circuit is completed (closed). There are also "normally open" (N.O.) switches in which the opposite is true.
Pretty much all security contacts are either N.C. or N.O., and all of the contacts in an alarm zone must be the same type. You can usually mix types among zones in the same system, however. Most all of these sensors are available for hardwired or wireless systems.
Common sensors include:
Pushbutton (plunger type) -- can be used in doors or windows
Roller ball -- similar to pushbutton
Recessed magnetic -- work like the magnetic above, but are drilled into the window or door frame, so they are invisible
Security screens -- a screen that replaces your existing screens that is connected to the security system
Passive Infrared Motion detectors (PIR) -- Pick up on body heat to activate an alarm
Infrared beams -- Break the beam and the alarm sounds (similar to the safety sensor on you garage door opener)
Pressure sensitive mats -- step on the mat, activate the alarm
Glass breakage sensors -- attach to windows and respond to vibrations if glass is broken
Infrasonic glass breakage sensors -- "listen" electronically for the sound of breaking glass
Window tape -- that ugly silver tape that detects broken glass
Smoke detectors
Heat detectors
Carbon monoxide detectors
There are many, many variations on all of the above mentioned sensors, and you can customize your system to be as complicated or simple as you choose.