Some homeowners have actually taken to spying on Realtors and potential buyers when they tour their home. Hidden monitors come in all shapes and sizes today. They can be disguised as smoke detectors, clocks, picture frames, etc. and are often called 'nanny monitors'. It's never happened to me - to my knowledge - but I know other agents who have experienced it. I've heard their stories and they were not happy.
While it may not be illegal (and I'm not sure about that), it just seems kind of shady. Would you ever use a spy camera to monitor people in your own house? What would you do if you were 'spied on' in someones home? [where: 75230]