We have a vacation house that was built in the early 70s, and there are two strange "outlets" in the house, one in the master bedroom, and one in a hallway in an addition (added in the early 90s). Sadly I don't have a picture. The outlets have two recessed round pins that are about 1/2 in. apart horizontally, and one of these "outlets" has a cover that attaches to these pins.I was thinking they might be some sort of phone jack or something, but I'm not sure. Any ideas?

2 holes sounds more like speaker connection jacks.Popular during the 70's.Do you have a wall mounted radio?

Brian is right. Sounds like a speaker set up with transmitter and speakers in one room and another set speakers in the other. Take the cover plate off and check the wires coming into box.

Chuck

Nope, no wall mounted radio. But between the addition and renovations, there are a lot of odds and ends around the house: blank cover plates, antenna cable, and amplifiers in random places, so who knows. When I get a chance to go up there I will take the covers off and look, thanks for the answers.