With the s9, that sensor is detecting the three-dimensional space in front of the Roomba as it moves forward. “It’s essentially scanning a volumetric space that’s roughly equivalent to the size of the robot,” says Brent Hild, a senior product manager at iRobot. It’s scanning that space using two planes of infrared light that project in front of it, with one plane higher than the other and both parallel to the floor. Those planes of infrared light bounce off the objects in front of the Roomba, allowing the sensor to know its distance from it. Thanks to those two lights planes, the robot can see anything ranging from about the size of a centimeter and up, Hild says.