So recently the alarm on my Multipla has started to arm itself after the doors being closed for 30 seconds, but doesn't lock the car. I have tried searching around for a solution but haven't been able to find one. If anyone knows of a way to fix this/ reset the alarm it would be greatly appreciated.

Quite a common FIAT/ALFA issue that normally manifests itself after a flat battery (i.e. stored settings lost).

From memory, you would re-set the settings via main dealer equipment, or disable the alarm with the little key on the side of the alarm siren.