A system recognizes the outline of an object that includes, at its edge, a portion including a rollover or a chipped portion. This can mean that in some situations gating is not used at all while in other occasions gating is used where the cycle length, burst length, number of preambles and offset are adjusted. The preferred metal compound is a metal carboxylate. The lock may be rechargeable by means of a solar cell 34 andor a knob operated dynamo.