You can find hidden cameras almost anywhere these days.  Hidden cameras are so small they are virtually invisible to a naked eye.  Whatever it is that you need to protect or whoever you need to catch in the act...

All the hidden cameras below are hand crafted in the USA. They are easy to use and involve minimum, if any, installation. Covert cameras can be used to ensure peace of mind and the safety of your family and business. Prevent employee, housekeeper or roommate theft and keep your eye on property and children by using hidden video surveillance cameras.

I'm sure you'll find just the camera you'll need. They are very portable...easily moved from room to room or place to place.