I woke up one cold morning to the car alarm going off. Seems the alarm went off by itself (in a locked garage) and I had to manually shut it off using a security key at the siren horn because the remote couldn't switch it off as normal.

After the siren quietened I turned switched it on again but the darn siren horn just won't work even though I can clearly hear 'clicks' at moments where I'd normally expected a chirp or two - e.g., went I lock or unlock the doors. This is some related relay clicking. Everything else about the alarm system otherwise appears to be working.

Does anyone know what I should do to get the horn alive again? Could it be some kind of built-in battery that's dead, a fuse or something else? How should I diagnose the problem?

It's one of those frequency hopping remote systems with motion detector that's now 14 years old.

Advice or speculations equally welcome!

Thanks!
Lucast