A door lock barrel with key is an essential component of a cars security system. In conjunction with several other components the door lock barrel allows the door to be locked and unlocked via a key from outside the vehicle.

The <Model> door lock barrel is housed within the door cavity, behind the door card, and presents a keyhole to the outside of the door. The door lock barrel is connected to the door lock mechanism allowing it to be locked and unlocked. In cars with central locking systems the door lock barrel is also connected electronically to the ECU, allowing all doors to be locked and unlocked from one location. Additionally, the ECU may be used to activate and deactivate alarm and immobiliser systems.

Door lock barrels can fail due to wear and tear including damaged or worn keys, corrosion, damaged wiring (where connected to central locking) or due to attempted theft.