Smoke alarm with expired batteries.
A year or so back after a very boozy party Mrs Gabber and I stayed in a friends spare bedroom. After a minute or so of getting into bed I heard the telltale bip of a smoke alarm warning that it needed its battery replacing. A quick search of the room found the offending item and I went to relocate it somewhere else.

It was at that point that our plan was hatched.

Our hosts hadn't yet gone to bed so I snuck into their bedroom hid the noisy little bastard underneath their bed and returned to my already giggling wife.

If anyone has heard one of these before it lets off a brief, loud but very intermittent high pitch squeaking noise. It's also very hard to locate if you don't know where it is as the sound is so sporadic and short.

I think it took the wife and I at least an hour to get to sleep as we spent so long pissing ourselves with laughter every time we heard the faint, telltale noise coming from their room.

Turns out my mate slept through it all he was so wrecked but his wife was on edge for most of the night.
( Airman Gabber Living life like a 70's BBC presenter, Mon 16 Jan 2012, 11:43, Reply)