I've got an old smoke alarm somewhere, and it's battery is running out, so it gives out a beep every now and then. And I can't find it and it's driving us crazy...

Any suggestions? For example is there an ipad app somewhere which can locate sounds like that? If there isn't maybe someone should come up with one, because I'm sure I'm not alone.

When my brother died and I had to sort out his place I had the same problem multiplied several times, because he had quite a number of alarms stuck away in various places, and they all kept beeping and sounding exactly the same.