equipped with four infrared Cliff Sensors that prevent robots from falling off stairs or ledges. The Cliff Sensors are located along the inside of the bumper
. If the Sensors become obstructed by dust or debris, the infrared signal is weakened
it shows how the roomba uses the infared sensors to detect cliffs and dropoffs. the robot expects to recieve signals from the floor and if the signals take too long to get back to the robot such as driving over stairs, the roomba will stop and go in a different direction