To many of us, our garage (or workshop) is probably one of the most important parts of the house. If a burglar broke in, we’d likely be more worried about our tools! [Ron Czapala] decided he needed an alarm system in his garage to keep his stuff safe, so he decided to build one from scratch.

The system makes use of a Parallax 4×4 keypad membrane, a MCP23008 port expander, a Parallax Propeller, a LCD screen, and a few switches to represent future magnetic reed switches located in the door and window.

Using circular buffers, the propeller has several states for monitoring the garage.

• Not armed — ignore all sensors
• Armed — system will react to changes in the sensors
• Exit delay — system has been armed, 45 second countdown has begun to allow you to exit the garage
• Window trigger — if the window is opened, the alarm will go off immediately (siren and strobe light)
• Door trigger — alarm will go off in 60 seconds if correct code has not been entered on the keypad

For a complete demonstration, check out the following video where [Ron] explains it all!

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