A lock is provided with an electronics module (30) by forming the lock with a body (10) and a separate unit (18). The unit (18) includes a locking mechanism (23) and is inserted and removed from the lock body (10), removal allowing easy access to the electronics module (30) without requiring a separate access. This gives increased security. The locking mechanism (23), electronics module (30) and body (10) can be replaced with compatible components.