Robot vacuums typically don’t fall down stairs because they’re designed to use downward-facing sensors to detect and avoid stairs, If it happens, it might be caused by the abnormal cliff sensor. The cliff sensor is a sensor that prevents the Robot Vacuum from falling. The Robot Vacuum has a total of 3 cliff sensors, which are distributed on the bottom of the left, right, and front. You may try the following troubleshooting steps: 1. Turn the robot vacuum over, and wipe the cliff sensor with a damp cloth. 2. Keep the robot vacuum upside down, and press the Start button to check if the main wheels stop spinning after a brief spin and an alarm sounds. NOTE: The robot vacuum is not suitable for black floors. If the issue still persists, please Contact Support.