"Alfred Hitchcock Presents" The Creeper (1956)

Ellen and Steve live in a New York neighborhood that is being terrorized by a strangler known only as the Creeper. Ellen wants a new lock for her apartment door in order to be safe. She becomes more paranoid until a locksmith arrives. As the locksmith begins work, Steve calls. He tells Ellen that the Creeper has been using his job as a locksmith to get into the homes of his victims. The news comes a little too late as the Creeper attacks Ellen and begins to strangle her.