Abstract: A seat belt arrangement selectively enables vehicle drivability when a buckle member carried on a restraint belt is engaged with a mounted buckle receiving mechanism. The buckle member is removable from the restraint belt, and may be hidden or carried on the person of the user when leaving the vehicle unattended, thereby providing a vehicle anti-theft feature. The detachable buckle plate member is advantageously keyed to the buckle receiving mechanism such that only a particular buckle plate member will operate a correspondingly keyed receiving mechanism with which it is brought into engagement. Such keying may be provided mechanically in the form of a special shape such as employed in the construction of standard keys, or may employ other recognizable identifying factors, such as digitized, audio, optical or other discernable discrete data communicated between the plate and locking members.