Question: I have a key-ring that flashes and beeps when I whistle- this is because I always lose my keys. I've worked out that it only works when I whistle at a ceratin pitch. How does it work?

Mark Roberts answered on 15 Jun 2010:

So how this will work is quite simple – so sound is formed of waves that move through the air – these waves have different frequencies depending on the pitch – the device itself has a thin membrane that will vibrate and this will work well at a particular frequency called the resonance frequency – this membrane will probably have a magnet attached and the movement of that will cause an electric current and hence a beep

so that is probably how it works and the reason for that certain pitch is that the waves it produces are the resonant frequency for the sensor

Hope that answers your qu – and if you want more info let me know