The traveling sprinkler. I've admired these for years and finally bought one last spring. This lawn sprinkler is water powered and uses the water hose for guidance. It is a very user-friendly device and has an auto shut off feature implemented as a plunger that is engaged by a ramp placed where you want the traveling sprinkler to shut down.
The mechanism is described in this HowStuffWorks.com article:
http://home.howstuffworks.com/traveling-sprinkler1.htm
