This project uses an ESP8266 for an motion detection based alarm system.
Parts used:

• ESP8266
• PIR motion sensor
• Relay for light
• Piezo alarm speaker taken from a window alarm system
• LDR resistor to measure the brightness and activate the automatic light activation

The alarm system is part of my home control system.
The alarm can be activated automatically by programmed on and off times or manually from a PC or Android tablet
The light activation at night is automatically activated by environment brightness
A still camera is triggered over WiFi to take a snapshot when an alarm is triggered
More information about the project on Bernd's development stuff