There's some wires you have to bury or staple around the perimeter of where you want it to mow.
It has some sort of ultrasound sensors in it for the lazy cat. One we saw mowing the lawn at the offices of Svenska Kullagerfabriken AB in Göteborg was demonstrated to us by a guy stepping in front of it with no shoes on and his toes towards the mower. The blades are well under the deck and protected by a big perimeter around it. The blades are only 8" but the length is about 2 1/2 foot long by 2 feet wide. If it tips over or is lifted by even a inch, the sensors on the wheels sense it and it stops within milliseconds.
He just stood there and when the sensors "saw" his foot it backed up a ways and took off in a new direction. The ultrasound sensors in it will make it stop if it encounters anything taller than 6". Otherwise it has a bumper sensor on it that it uses to navigate around trees and so on to "learn" where the obstructions are.
It navigates by means of radio signal from its base station with a guide wire and perimeter wires. If you have flower beds or something that you don't want mowed down you have to put the perimeter wire around them. The thing runs around and mows for about an hour, then returns to its charging station to get charged back up. The high priced one has a solar panel built into the top of the mower and if the sun is shining it will mow continuously for how many hours a day you want it to mow. Rain doesn't bother it - it goes out in the rain too. It can handle standing water up to 3 inches deep. But if it encounters water deeper than 3" it back out of it and goes someplace else. The expensive one can handle grades up to 35%. But if you have any holes deeper than 3" in your lawn, it can get stuck.
They are very high quality units, as with most anything made in Sweden. There are three brands of robotic lawnmowers on the market - all made overseas. The Huskie is made in Sweden, the RoboMow is made in Israel, and the LawnBott is made in Italy by Zucchetti. Huskie has a video on them on YouTube:
They also have one on what's required to install it:
My wife does the lawn mowing and trimming, and she'd definitely like to get one.
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Chris