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!

Arduino Based Wireless Intrusion Detection Using IR Sensor and GSM Intrusion Detection Systems (IDS) strive to catch computer system intrusion & utilize by any garnering and analyzing data.

The system here uses a cheap Arduino board, a few sensors, and a magnetic contact switch. It’s then hooked into the Adafruit IO and connected to IFTTT, so you can set up alerts in any way you like.