It's official: you can never be sure someone isn't watching you at all times.
Just take a look at this tissue box. It looks benign enough.
But inside is a camera that takes color footage in the daytime and black and white footage at night, all at a resolution of 720x480 with a framerate of 30fps.
It uses SD cards to store footage, and can be programmed to activate automatically at a particular time. In fact, there might be one somewhere in your home right now. Probably not, but there might be.