my gt car alarm immobiliser failure?

The GT car immobiliser on my wifes pajero 1995 will not activate the ignition, even with new batteries, and she has to keep plugging in a reset key under the passenger side glove compartment - a real pain in the ass with three kids around. Does anyone know how to fix the immoboliser so that it is bypassed completely , as it is unlikely that the car will be nicked because it would cost too much in diesel to make a get away. Many thanks