Alarm problem
 

My partners s40 2008 has started to set the alarm off in hot sunny weather the only time it doesn't go off is if i set the interior sensor to be off has anyone come across this and if so how was it fixed its driving me insane tia

It's possible that the battery in the siren unit has failed. Search on here there are plenty of threads on the issue and how to resolve it.

If it had of been the battery in the siren unit surely it would still be activated when interior sensor is switched off