This circuit is an alarm for the home or car door and a lot more. It employs a magnet and reed switch to trigger the circuit; when the magnet is moved away from the reed switch the alarm is triggered. An integral piezo sounder produces the alarm sound (100dB). And a PLUS a relay capable of handling up to 10 amps AC is included and may be connected to turn on or off an appliance light or external alarm sounder etc. Therefore the circuit could be used to turn on a light whenever a basement or garage door is opened.