The central locking unit on your model of laguna is built in to the immobiliser unit (decoder). The unit is clipped to the side of the fuse box.... look under the dashboard on the drivers side so you are looking at the underside of the fuse box, between the fuse box and the body of the car you will see a small black box, push up on the box to un clip it then pull it down to unplug it. The decoder unit is coded to your car and a new one would need programming by a renault dealer.