A lock for a helmet is disclosed consisting of a lock which is mounted integrally with the liner of the helmet along an edge of the helmet, with the key access and shackle facing outwardly. The shackle is a three-position shackle, capable of being locked in one position such that the shackle extends beyond the periphery of the helmet in order that the helmet may be locked around a suitable object and is lockable in another position such that the shackle is flush with the top face of the body of the lock. An open position of the shackle allows the shackle to swing freely in order that it may engage such a suitable object and the shackle be subsequently locked into the first locked position.