Magnet on a string?

I once carried a manly little handbag around with my stuff in it and once left it on top of the car and drove onto the freeway and home. I got a call half an hour later from someone who lived only a quart-mile away from me, wishing to return the thing, which he had boldly stopped to pick up from the on-ramp. It was intact and I have never forgotten his act of human kindness.