dartymoor: I checked this cache today and the chirp was silent.
There's no chance of retrieving it to get at the battery (it fell inside the root system of a tree growing in a bank when I first put it out), and the secondary coords were lost when somebody drove through the footpath sign, which still hasn't been replaced.
So, archiving as a beacon cache as I won't be replacing the chirp.
Thanks all, an interesting little diversion for a while.