Ford Focus Owners Manual: Principle of operation

Engine immobiliser

...

Coded keys

Note: Do not shield your keys with metal objects. This may prevent the receiver from recognising your key as a valid one. Note: Have all of your remaining keys erased and recoded if you lose a key ...

More about Ford Focus:

Ford Focus Roof Opening Panel Shield
Removal and Installation NOTE: The roof opening panel motor must be initialized when repairs are carried out on any part of the roof opening panel system, including: whenever the roof opening panel motor has been removed from the roof opening panel system, the roof opening panel glass has be ...