The usual one: check all the doors lock/unlock with the key; check the boot light is going out (and adjust the mount plate if necessary); make sure the switch in the bonnet by the radiator is ok.
Don't forget that, not necessarily as you'd expect, the alarm and the locks aren't really attached to each other. The alarm keeps an eye out for things changing like doors opening, and when it gets a plib it can lock and unlock the door. But the lock signal isn't replicated to the alarm; doors unlocking is almost always the lock circuits, i.e. one of the internal switches in the door locks, or the boot light.