Why won't my Mazda 323 1993 hatchback start and doesn't make noise?

I have similar problem with my 1993 Mazda 323 and I'm told its a problem with the immobiliser. Seems that the alarm system is hard wired into the ignition and fuel systems of the car and one part of it has perished with age so the whole thing is kaput

Do you know where the sensor for the alarm is on your car, because I can't find it on mine!