Three main states of the system can be distinguished: disarmed, armed and alarm. When disarmed, the system is like a guard who has been ordered to pay no attention to the people entering or leaving the site. But if the guard receives an order not to allow unauthorized persons into the premises, the situation will change. It is much in the same way with the security system that has been armed. From the moment of arming, an alarm will be triggered whenever presence of people is registered in the premises. The security alarm system includes a number of electronic devices. To create a simplest system, you will need the alarm control panel, control device, detectors and sirens.
Also, the telephone line and a PC computer, which is already present probably in most households today, will prove useful.
An example of alarm system