An Arduino based remote buzzer project by Flute Systems:
Base station uses an Arduino Pro Mini 5V. The reason for having 5V in this circuit is the TM1637 7-segment display. We’re using a 5V active buzzer module, two wires – signal and ground. On the left are the Adafruit PowerBoost 1000C for 5V and the green Pololu switch mode voltage regulator board for 3.3V for the radio module. The Base Station runs for ~5 hours off a 2000 mAh LiPo battery.
See the full post on Flute Systems blog.