Google it Ray. The coil around the steering lock barrel induces a current in the chip and asks the chip to identify itself. The chip provides a code which disarms the immobiliser.
The immobiliser remains off until the key is removed and after about twenty seconds it re-arms.
Fancier chips also receive a new code each time they are used but I don't think this happens with the Ford system.
Thanks Dave, the wonders of modern electronics
.+8 Now gone for a 1800 4/4. Duratec in bright yellow.
