P1571 - Immobiliser

[MaxHeadroom]

My 996.1 coupe decided not to start yesterday and having got it home with a tow, I've started to investigate.
My code reader tells me that it's registered fault P1571 - Immobiliser. I don't have access to a Durametric to get more detail than this. When trying to start the car all the normal lights on the dash come on but when turning the key the last bit the starter doesn't crank. I also tried to push start the car but it wouldn't go.

The alarm module has not been allowed to get wet. Also when first trying to start it when the problem first occurred there was a mild smell of burning electrics in the car. If anyone can provide guidance on how to test the ignition switch and the wiring to the alarm module and DME then I would be very grateful. I don't want to just send off the alarm module for an expensive diagnosis/fix until I've discounted the switch and loom.