The Roomba is powered by a removable NiMH battery, which must be recharged regularly from a wall power adapter. Newer second- and third-generation models have a self-charging homebase that the unit searches for at the end of a cleaning session via infrared beacons. Charging on the homebase takes about three hours. Four infrared “cliff sensors” on the bottom of the Roomba prevent it from falling off ledges such as stairways. Most second- and third-generation models have internal acoustic-based dirt sensors that allow them to detect particularly dirty spots and focus on those areas accordingly. Fourth-generation models have an optical sensor located in front of the vacuum bin allowing detection of wider and smaller messes. Many second- and third-generation Roombas come packaged with infrared remote controls, allowing a human operator to “drive” the robot to areas to be specially cleaned.
Some higher-end 500, 700 and 800 series robots are compatible with Virtual Wall Lighthouses, which use radio signals to communicate. These more advanced accessories confine a Roomba to a fixed area to be cleaned, yet allow the robot to later proceed to the next space to be cleaned.
There are several types of dust and debris collection bins for the 500 series robots. The standard vacuum bin incorporates a squeegee vacuum. The high-capacity sweeper bin does not include a vacuum, but has greater debris capacity. The Aerovac Bin directs suction airflow through the main brushes instead of using a squeegee, which is thought to keep the brushes cleaner.
All Roomba models are disc-shaped, 34 cm (13″) in diameter and less than 9 cm (3.5″) high. A large contact-sensing mechanical bumper is mounted on the front half of the unit, with an omnidirectional infrared sensor at its top front center. A recessed carrying handle is fitted on the top of most units.
As of 2015, there have been six generations of Roomba units: the first-generation Original Series, the second-generation 400 & Discovery Series, the third-generation Professional & 500 Series, the fourth-generation 600 Series, the fifth-generation 700 Series, and the sixth-generation 800 Series. All models have a pair of brushes, rotating in opposite directions, to pick up debris from the floor. In most models, the brushes are followed by a squeegee vacuum, which directs the airflow through a narrow slit to increase its velocity in order to collect fine dust. A horizontally mounted “side spinner” brush on the right side of the unit sweeps against walls to reach debris not accessible by the main brushes and vacuum. In the first generation of robots, the dirty air passes through the fan before reaching the filter, while later models use a fan-bypass vacuum.