Here is an ultra simple Arduino Night Alarm project wired around a handful of inexpensive and easily available components. One advantage of using Arduino as a security system is the flexibility!

TK has combined a PIR with an Arduino to create a smart safety light for the house or workshop. Follow along as this gets built out into a more extensive project.

Present consists of just a PIR sensor and Arduino in a 3D printed enclosure to snap onto your monitor.

For his sensor, [Felix] is using a Moteino, a very tiny Arduino compatible board with solder pads for an RFM12B and RFM69 radio transceivers. These very inexpensive radios – about $4 each ...