Bought a factory refurbished one despite the legendary dubious quality on these things. It was the BIG model and I have one little cat. It worked fine for 5 months, then it started missing 50% of the cat's visits. I took it apart and cleaned it thoroughly, again it worked fine for a month.  Then it just stopped raking at all. I called customer service, who tried to tell me that the amount of time you left the device unplugged from power made a difference in the "level of reset" it goes through. For example, unplugging it for 2-3 minutes made it do something different than unplugging it for 10+ minutes.