I fear we may be about to find out.
There is an incredibly loud beep coming, we think, from the shed of a slightly deaf elderly neighbour. I've had a little walk along the street and all the houses have people home in them (judging by lights, presence of car etc), and no sign of problems. The beep is loudest at the corner near her shed, and quieter by the front of her house so I'm sure it's not in the house.
Trying to alert her would a) alarm her and b) disturb more people than the beep currently does.
How long do we think?