I am trying to identify an old film, or possibly a 30 minute TV show. It involved two aliens who looked like men going to a boarding house on Earth. The aliens could control a force field shaped like a large rectangle and possibly other things. They had a rubber-like half dome thing in the palm of their hand. When they pushed it with their middle finger curling back it activated a force field.
The boarding house lady discovered this and killed an alien and removed the little half dome thing and put it in her hand and activated it. But when she tried to deactivate it, it wouldn't. She realized this and threw the half dome thing down.
The other alien then came and I think used a needle type thing and opened a corner or little section of the force field just enough to put his hand in and retrieve his alien friend's dome thing. The force field then shuts back and traps her forever and the alien walks out the door.