During an evening of babysitting, high-school student Jill Johnson is terrorized by a caller who keeps asking "Have you checked the children lately?" When she calls the police, they inform her that the calls are coming from inside the house.
A babysitter takes a phone call. The voice says: have you checked the children? The first twenty minutes were so effective they were remade twice. The whole film deserves the rewatch; the opening rivals any horror short ever made.