Cameras

Cameras are very useful and the only limits are your imagination. They can almost always be used to give yourself an advantage or put you in a disadvantage. If you're selling a home, it doesn't hurt to setup a few cameras. Finding out what the potential buyers are thinking in advance will help massively during the negotiation phase.

The same is true if you're buying a house. Try to avoid any comments that would show your opinion on certain matters (especially the pricing). Both positive and negative comments will have consequences.

Cameras are also very effective in dissuading robbers and just information gathering in general.