Build this SCR based intruder alarm using cheap off-the-shelf components. It's suitable for all types of premises - including caravans, camper vans and mobile homes.
Main Circuit Board
This is a photograph of the main circuit board of the SCR Based Burglar Alarm. It features automatic Exit and Entry delays - together with a timed Bell cut-off and Reset. It's designed to be used with the usual types of normally-closed input devices such as - magnetic-reed contacts - micro switches - foil tape - and PIRs.
The basic alarm has a single zone with "Exit/Entry" delays. This will be adequate in many situations. However - larger buildings are best divided into zones. The modular design means that it's easy to Add Any Number Of Zones to the system. These "Instant" zones may be triggered by both normally-open and normally-closed input devices.
Four-Zone Expansion Module
You can Add Any Number Of Zones to the system. This is the circuit board of a Four-Zone Expansion Module. It's designed to be used with all the usual types of normally-open and normally-closed input devices such as - pressure mats, magnetic-reed contacts - micro switches - foil tape - and PIRs.
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