Ever wish your home or office had plane-style occupancy lights so you know when the toilet is in use? Some crafty hackers in Tokyo made this dream into a reality.
Their attractive setup incorporates a motion sensor in each bathroom hooked up to a wireless Arduino board. The board transmitted the room's occupancy state to an array of LEDs that could be mounted to a wall and show anyone the current status of the bathrooms on three floors of the building.
This build was very specific to their office arrangement, and there are a lot of ways you could go about tackling it, but it's great inspiration for anyone in need of a fun and practical project (or who is sick of toilet interruptions). Check out the source link for more details on how they did it.