Chirruping

No, this is not a blog entry about birds. Two days ago I was downstairs and heard a strange sound from above - very brief, less than a second, but shrill. My instinct was that it was a bird on the roof, but then I realised that it wasn't quite natural. My next thought was that it must be someone next door - they're often making drilling / sawing sounds as they've been doing some rennovations to their house. I came to the conclusion that they were sawing metal pipes (they did have their gas heaters removed the week after we had our central heating put in). Only when the sound began to repeat at regular intervals of about 3 minutes or so did I realise that it was coming from our house.

It turns out that when the battery is low our smoke alarm 'chirrups' (it actually uses that word on the alarm). The smoke alarm was here when we moved in and to my knowledge it's not happened before. I think every house I've lived in has had a smoke alarm, but this is the first I've ever heard chirrup.