Thank you for the response. The alarm has stopped going off now of its own accord, so the immediate problem has gone away. However, I'm still none the wiser as to why it happened in the first place, and worried that it could happen again. I can't be the only person this has happened to -- there must be someone out there with experience of Mitsubishi alarms. In particular I'd like to know why it stopped, and whether there is a built-in time limit on the length of time it will continue before it resets itself, which is what it seems to have done. So, please keep my question open. In any case, I have paid £15 to get this far and would like my money's worth, please.