When you start up the Discovery, either with the remote or by pressing a button on the unit, it beeps a little salutatory tune and embarks from the docking station. It cuts a seemingly random path, zigzagging across the room and bumping around in corners. The path isn't really random, though--according to iRobot, the Discovery senses information about its environment 67 times per second and adjusts its path so that it will cover the whole area before returning to base. If you set it on Clean, it will cover just one room, and then go back to the docking station to charge when it's decided that cleanliness has been achieved. To cover multiple adjoining rooms, set the Discovery on Max, and it will run until the battery dies. There's also a Spot setting that causes the device to wheel around in little circles over a three-foot-diameter area in order to handle particularly nasty patches. The Roomba Discovery is pretty good at the things it's made to do: It can navigate tight spaces without getting stuck, and although it's not one of the most powerful vacuums around, it does a good job of picking up the usual household debris--including cat-fur tumbleweeds. Whenever the unit hit a really grimy spot on my hardwood and tiled floors, its blue Dirt Detect light illuminated, and it spent enough extra time on the space to pick up all the filth. It didn't choke on the paper clips and other small items I arrayed in its path, and it obeyed the restrictions of the Virtual Wall units that I set up. I was also pleased that it didn't knock over any lightweight items or seem capable of doing any damage to objects it bumps into. As a bonus, the Discovery provided a unique interactive experience for my cats.
Too good to be true, you ask? After running the Discovery several times around my hardwood and tile floors, as well as over a small piece of carpet, I found a few significant drawbacks in its performance. The first one is speed. When I restricted its activity to an 8-by-9-foot room with a hardwood floor and a 3-by-4-foot entryway, it took about 25 minutes to complete the job. That's at least 5 times as long as it would take me to clean that space thoroughly with a regular vacuum. Of course, I was in the kitchen cooking dinner while the Discovery was slaving away, so you could also look at it as having saved me 5 minutes.
Unfortunately, the Discovery isn't completely thorough either. Despite its high-tech minesweeping algorithms, the unit missed some spots, leaving about 10 percent of the dirt. That's pretty good, but I still had to finish the job with my regular vacuum. Even if 90 percent is close enough for you, you may not want to hear the Discovery running for the length of time it takes to clean a room, even though it's relatively quiet as vacuum cleaners go.
Another drawback is that the Roomba Discovery isn't above being stymied. After all, it's a machine. During one run, it fell into a sort of holding pattern in a corner that had a wall on one side and a couple of coffee table legs on the other. It spent about 15 minutes spinning around in that space, refusing to head for the open areas on its two other sides, before calling it a day and returning to its dock. The Discovery also failed to respond to the remote on occasion, going into sleep mode instead of swiveling around as I had commanded it to do. Plus, the Discovery doesn't have any attachments, so you can't use it to clean upholstery or carpeted stairs.
If you have problems pushing a vacuum cleaner around for physical reasons or simply hate vacuuming, the Roomba Discovery might be a good investment. Don't give away your old, conventional vacuum cleaner, though--you'll need it to clean that last 10 percent.