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 Luggage Compartment Lid Latch
  Item Part Number Description 1 — Luggage compartment lid latch electrical connector (part of 14A584) 2 W707137 Luggage compartment lid latch nuts (3 required) 3 5443200 Luggage compartment lid latch Removal and ...