Help with old movie title

Hey, new here, but was hoping someone could help figure out the name of a movie I saw at the theater as a kid. It was either late 70s or early 80s. I thought it was called the clock behind the wall. Apparently not. There was someone killing people and the police were trying to figure it out. In the end they thought they had, but as they were leaving a room in the house, they heard an alarm clock going off, it was coming from behind the wall where the killer had put someone. I know, long shot! But I'm hoping! Thank u