Headlights coming on

Some of you may have seen a post from me a few weeks ago regarding a battery drain issue. Long story short - I put a new UPC in (albeit a used one) and replaced the battery and everything seemed to be okay. Now it has just tonight starting playing up again. The headlights and fan keep coming on sporadically of their own accord whilst the car is locked and the light stalk is switched off. If I go out with the key and unlock it they turn off again. It’s done it 3/4 times now within the space of 20-30mins. I have disconnected the battery for now as the fan is loud going full-chat and will wake everybody up.

Any ideas what it may be? Anyone had a similar issue?
 
iirc upc are coded specific to the car and cannot (in theory) be used on another...