Thanks for reply. Yeah I have tried opening passenger door, my drivers door doesn't have a keyhole, instead it has two LEDs also red and green. They flash green when I use the fob to open the car, and red when lock. When I try to start they flash alternative red/green.

In the 1994-1997 W202 C-Class how does the flip key fob communicate with the immobiliser? Is there a chip in the key that relates the code via the ignition barrel? I was told the immobiliser unit is under the passenger footwell.