Roomba -- a self-navigating vacuum cleaner with wheels for feet, infrared sensors for eyes, and a flair for picking up dog hair -- is the most successful consumer-market robot in history. Its maker, iRobot of Burlington, MA, has sold more than 1.5 million* of the Frisbee-shaped gadgets since their debut in September 2002. What's more, many owners swear by their Roombas -- they've bought units for other family members, written gushing product reviews on shopping sites, formed fan clubs, complete with message boards, and even decorated their Roombas as pets.

Given this level of success and enthusiasm, one might have expected Roomba copycats to be flooding the market. Almost four years later, however, the only product that's attempted to follow in Roomba's tracks is the same company's Scooba, an automated "robomop" that carries its own cleaning fluid and scrubs, washes, and dries hard floors such as hardwood, tile, and linoleum. Since iRobot is launching the Scooba in this quarter, it's too soon to tell whether it will make a splash.

In truth, the idea of robots in every home seems further away today than it did four years ago. The reasons are not entirely clear. It could come from a lack of interest among consumers, a lack of imagination among product developers, or a lack of tasks that could be done well by robots.

Helen Greiner, one of three co-founders and current chairman of iRobot, believes the market for home and office robots is about to grow. She started iRobot in 1990 with fellow computer-science student Colin Angle and Rod Brooks, a professor in the MIT Computer Science and Artificial Intelligence Laboratory, and she holds two degrees from MIT, a bachelor's in mechanical engineering and a master's in computer science.

Technology Review: iRobot's Roomba vacuum cleaner proved that there is a market for home robots. Yet Roomba has been on the market for almost four years, and neither iRobot nor any competitor has come out with consumer robots for other types of jobs. Why not?

Helen Greiner: We have. We just launched our floor-washing application, the Scooba. It's a completely different robot. Vacuuming and floor washing are very dissimilar chores around the house.

TR: Of course, my mistake. What I'm asking is: What makes the Roomba special -- and why hasn't anybody else been able to replicate the success you've had with it?

HG: The real difference between the Roomba and robots that came before is that it's a very practical system at a price that meets consumers' needs. It's at about the same price point as a vacuum cleaner. And you don't have to push it around. It goes under furniture and beds. Its value exceeds the price customers pay for it, and I don't think the robots that cost $1,500 or $2,000 did that.

TR: To keep the price of the Roomba reasonable, you must have had to omit some features. How did you decide what to include and what to leave out?

HG: It was tough. As you know, we come out of MIT and are a bunch of technologists. When we put out the first Roomba, it was $199, and basically you turned it on and it did the [vacuuming] job for you. That's what consumers needed. We knew we could make things like remote controls and a charging station and the scheduling feature, which are really great stuff, but it would have increased the price.

Then, as people got used to the idea that they could have these things in their homes at a reasonable price, they started coming to us with ideas -- like, "Wouldn't it be cool if it could recharge itself?" or "Wouldn't it be great if I could get it to turn on every day at the same time?" So we brought out those additional features. [Today, the Roomba comes in four models, from the high-end Roomba Discovery for $300 to the Roomba Red for $150. -- Eds.]

* Correction: Due to a transcription error, the original version of this story said that iRobot had sold 5 million Roombas. The actual number is 1.5 million.