Don't let anyone sneak into your room undetected! Build your own Intruder Alarm to keep out those pesky brothers & sisters! And while you are at it, explore how a magnet sets off this cool build-your-own intruder alarm.
It's a great project for exploring how a magnetic switch works in an electric circuit.
Johnco are the proud Australian wholesale supplier of award-winning toy brand 4M.
![](https://i.ytimg.com/vi/goh5Lyw6seM/maxresdefault.jpg)