an Entity references as follows:
The Sitter is a 1977 American horror-thriller short film directed by Fred Walton on which his 1979 feature film When a Stranger Calls is based. It is a suspenseful retelling of the classic urban legend of "The babysitter and the man upstairs" about a babysitter who is menaced by mysterious and frightening phone calls which are finally revealed to be coming from inside the house.