The idea of an annoying beep device it’s pretty original and I’m sure it works on everyone. So here is how it works, the thing is damn small because it only contains the ATTiny13, a piezzo speaker a resistor and a capacitor, thus beeing easy to hide; you carefully hide the device into a friends house. The device will start emitting a beep sound at random intervals of time. The time between beeps is anywhere within half an hour to nine hours.
Your friend will start looking for the source of the beep among his gadgets like mobile phones, tv, etc, not knowing that the beep is coming from the prank device. Just imagine yourself into this situation, it will drive you nuts :). And there’s another feature of the device, the small battery will last forever because the device only draws 200uA.
Annoying Beep Prank Device: [Link]