Here’s a tiny pcb that produces an annoying sound using a piezo buzzer and a ATtiny13 microcontroller.
It uses an LED, piezo buzzer, ATTINY13 Atmel microcontroller, a very small amount of Arduino code, and a coin cell battery that should last about a week.
Battery life could be improved, with longer sleep times. The device has but one function: sleep, then wake up periodically and blink and chirp, then go back to sleep.
Firefly – an annoying little thing – [Link]