I used a button cell clip as frame, on top of it a 20mm 8 ohm, 0.1 watt speaker and on the side a ATtiny85 socket. Pins 4 and 8 of course wired to the cell, and pins 2 and to the speaker. The speaker runs on Timer1 in Fast PWM mode. Counter runs to 145, prescaler set to 1. At 1 Mhz this corresponds to 6900 Hz, which seems to be the frequency where the speaker gives the most sound pressure. The toen sounds for 100 ms, followed by a 32 seconds silence. The bug is so small en mostly black that it's really hard to find.
