The Roborock E4 is a robot vacuum cleaner that is considered a good option for smaller homes, like apartments or condos. It has an app that allows you to start and stop the unit, set the vacuuming power, and schedule cleanings. The E4 has sensors and can "dead reckon" its location, which helps it navigate your home without aimlessly bumping into things. The vacuum is noted for its strong build quality and good battery life.