The mower's path is constrained by a hidden wire boundary that defines the limits of your yard.
Because the robot uses an electric motor, the cutter spins at higher RPM than gas-powered mowers, yet produces far less noise (and no fumes). The mower detects ambient moisture, so it will return to its docking station if it is raining. As a safety measure, the unit automatically shuts off when lifted in the air.
All of this means you can program the robot to automatically trim your lawn on any day and pretty much any time you like. The robot will return to its docking station when it has completed cutting your lawn or when it needs to recharge itself.
Check out all the details on the Robotic Lawnmower.