Here is an ultra simple Arduino Night Alarm ... our system requires a “Logic High (H)” level input to wake up. The best sensor you can use to detect an intrusion is the Passive Infrared (PIR) Sensor.

When the motion sensor detects movement, it buzzes the other Arduino. Combine that with a text messaging alarm system and you've got a pretty cheap and easy way to keep an eye on things at your house.

You can connect any intrusion detection unit (such as a light fence or a motion sensor) to the input connector J2. Note that an active-low (L) at pin 1 of connector J2 triggers the security system ...

When something passes in front of a PIR sensor it ... to PIR Pin “Alarm” PIR Pin “Alarm” connects to Arduino Digital 2 The code for the active low Sparkfun style motion detector looks ...

We've shown you how to create a web streaming, motion-detecting surveillance system ... the Arduino platform. All you need is an Arduino, a motion sensor, a few wires and headers, and the code ...

For his sensor, [Felix] is using a Moteino, a very tiny Arduino compatible board ... sees something it transmits a code the base station where the ‘motion’ alert message is displayed.