[herlichka]

Occupancy sensors are a very efficient way to control lighting, but you will need to do a fair bit of research and be willing to do a lot of fine tuning in the application. As a former "material guy" for an electrical contractor I learned a lot about these products.
-Some models feature controls ( on-off-auto ), decide if you want people to be able to manually turn lights on-off.
-Be sure that the one you choose is compatible with the type of lighting that you want to control.
-Some models have to be reset after a power failure, they may revert to the "on" mode, or the time delay may change. If they are in a difficult place to access, such as near the ceiling, you may regret installing them.
-The application, siting, may be the most challenging issue. People are not the only "things" that can activate sensors. Beware of things such as sunlight shining through a window, setting up thermal air currents, forced air heating and cooling, leaves on potted plants moving, even the controlled lights themselves may set up thermal air currents that can trick the sensor into thinking someone is in the room.

If you are careful to select the correct unit, and patient enough to tweak the install, then these are an awesome energy saver. If you talk your local electrical supplier, and ask the right questions he can direct you to the right products. Do your homework, there are many products available with specific features, that are not stock items at the big-box-stores, but can be had at similar prices, often overnight, from your electrical supplier.
I hope that this is helpful.
I just re-read your original post, and thought of something else; restrooms can be additionally tricky, the sensor has to be positioned so as to sense the presence of a person in the room AND in the stall, the lights may turn off if the person in the stall is quietly taking a long time, and this is a situation where someone may turn the sensor to "on" if it is equipped with manual switches.