The control unit may be powered by electricity that runs in your home, or by battery power. Some systems are set up so that if the power in your house goes out, a battery backup will kick in and run the control unit until power is restored. Once the power flips back on, the backup battery system will automatically recharge. The sensors, or switches, are the second
part of the security system. The most basic alarm systems have these sensors fitted in the frames of windows and doors so that if they are opened, the circuit is broken and the alarm is triggered. Some are installed in a way that allows
them to detect if someone tries to break in through a window by shattering the glass or removing one of the panes.