iRobot's new 'robust' Roomba - While previous incarnations of the Roomba did allow for virtual walls to restrict where the robot could travel, the Roomba 560 works by what iRobot refers to as lighthouses. These are beacons that can be put in places like doorways to automatically communicate with the Roomba whenever it's on. Each lighthouse beacon takes two C batteries and can instruct the Roomba to finish cleaning one room completely before moving on to the next and then guide it back to its home base for recharging when it's done. As with the virtual walls, the lighthouse beacons can also bar the Roomba from a room completely. Using the lighthouse system, the Roomba 560 takes about 35 minutes to clean one room, according to Preneta.