I purchased this model 1 1/2 years ago following my knee surgery. The unit worked beautifully the first 3 times I used it. When it started doing crazy things, I just unplugged the unit and when I was fully recuperated, made attempts to get the unit working. I emailed the company and they sent instructions to me as to how to re-set the unit. We went through this at least a dozen times to no avail. My unit would take off from the base and within 12 inches of the base, did a little circle dance then marched itself back to the base. iRobot tells me they have no service available for the unit and to this day, the company continuously sends me emails about purchasing a new model. I purchased the model for $150. back then and it was a total waste of my money. It has been packed away in my garage ever since. A one star rating is too high but there is no zero.