As I type away here, in an office with an unnaturally clean carpet, I am alone in the house. Everybody is away on an errand or at school. Nonetheless, the annoyingly long downstairs hall is being cleaned.

The dust bunny, an animal of unsavory appearance and miserable parentage, is becoming an endangered specie in our house.

We have entered the 21st century as it was supposed to be in the science fiction stories of my youth: we have a robot working for us. It talks not, neither does it listen. But it does sweep and vacuum floors.

It's even entertaining in its own way as it bumbles about following marching orders that only it can hear. Sometimes it spins in ever-widening spirals. Sometimes it marches in determined straight lines across the floor. It can sneak along a wall, a little brush poking out to get dust bunnies trying to hide in corners. It slithers under furniture, going where no man has gone before.

It can be frustrating to watch it work. There might be an obvious piece of debris on the floor, and it just ignores it, wandering this way and that, missing it to right and to left. It's enough to drive you crazy. Eventually, it will get it. I am not perfectly sure how but, like the pot that boils only when you go to answer the telephone, it covers the whole room in its dance. So you learn not to watch it. You just put it into the room, turn it on, press the go button and leave (it plays a brave little fanfare as it goes off to battle with Mr. Dirt). Turn out the lights if it's night; it can work in total darkness. You can watch if you want, especially if you are fascinated by the dim green glow on its topside reminding you of a demented oversize firefly trying to escape. And if you leave a door open, it will escape and keep on cleaning until its rechargeable battery gives up the ghost.

It is pretty clever about getting itself out of awkward corners, but it is utterly defeated by a rubber band left on the floor or tassels on a rug. It will get itself wound up in them and sit there making forlorn little beeps until you come and rescue it.

When it's done, it stops by itself. Then you pull out its small basket and dump the debris into the dustbin. The first time I did any room I found myself emptying the basket more than once before the room was finished. After the robot had established a basic level of cleanliness, it would typically pick up only half a basket at each weekly cleaning. It is so easy that I have been known to let the robot do the cleaning more than once a week, a phenomenon previously unheard of in my house. It is not perfect, and it doesn't get the tops of the molding, so a bit of help is needed. But what it misses is so minor and takes so little time to fix up, that I actually have been known to go and do it.

As vacuum cleaners go, it is neither the cheapest nor the most expensive. It sells for $200. But the Roomba (that's its name, really) is worth it, even if it won't pick up spills. When it comes to number of cleanings per vacuum cleaner dollar, it is a big win. We've had ours for a four months. It has become one of the family, we all like it. Except the cat, who finds another room to hang out in when it's working. We would not like to have to go back to things like banging clothes against rocks to clean them, washing and drying dishes by hand, rubbing sticks together to start a fire to cook supper, or having to push a stupid vacuum cleaner around a floor.

We've got better things to do.