Spotted while checking out the Environmental Home Center the other day, the WattStopper Occupancy Sensor is a sensor that turns lights on automatically when you enter and off when you leave a room.

Pretty useful for certain bedrooms, bathrooms and hallways as it promises to reduces lighting usage by up to 50%, and has functions like adjustable time delays and daylight sensing and even an optional nightlight feature.

Plus, they even work with fans and fluorescent lights (not all sensors do). Cool.