- Like home alarm systems, home security systems keep tabs on the well-being of a home through the use of door, window, motion and vibration sensors installed throughout the house. At doors or windows, sensors work by magnets; they register when the magnet attached to the door or window has been separated from the magnet attached to the door or window frame. When sensors indicates that a door or window has been opened, that vibration or breakage has taken place at a window or that motion has been detected by an infrared motion sensor, this status is registered with the security system's main control center. If the security system is unarmed, the activity is simply displayed on an output device such as a digital keypad. If the homeowner has "armed" the security system, the activity is registered and a siren and/or strobe light is activated.
- When the homeowner "arms" the security system and the system's control center registers activity, the system not only sounds a siren but contacts a monitoring agency such as ADT, Monitronics or Brinks. Traditional security systems use a modulator/demodulator, or "modem," to dial the monitoring center on a telephone line and provide an electronic detail of the activity that has occurred. More advanced security systems also have the ability to use a cellular telephone connection if the telephone line is unavailable.
- When the monitoring company receives an indication that an alarm has occurred, the company first attempts to contact the owner of the home. If the owner fails to answer or if the owner does not know a predetermined password, the security company also notifies the local police or sheriff's department. Some security systems also register and notify the monitoring company of smoke alarms triggered in the home, in which case the monitoring company immediately dispatches the appropriate local fire department.
