Alarm going off randomly

The alarm in my '96 MGF goes off for no apparent reason. Sometimes it happens a minute or two after the car has been locked, sometimes several hours later (a real pain when it sounds in the middle of the night).

The wiring at the LH hinge in the engine compartment looks OK.

Any good ideas where else should I look for the fault?

The alarm does not go off when i open the front compartment which I think it used to do before.

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