The Roomba (about £800 but there are several models at different prices) doesn't try to leap to its death down the stairs, it just stops and bleats for you to move it to safety.
One morning on a day when it was programmed to vacuum the downstairs rooms before I was up, like having a maid to get the house nice and clean for you, I found the study/diningroom door closed and went in to investigate. There was Roomba, sitting silently and unhappily in a corner. It must have entered the room through the half-open door, hoovered carefully all over, and then approached the door from the wrong angle and pushed it shut! It has spent all its charge on trying to find a way out and back to base camp and the charger. Since then I have made sure all doors are wide open when I want it to work unsupervised.
Later that day I went back to the study to use the computer. It wouldn't start - seemed quite dead! Tried everything, then noticed that the switch was at "off" on the extension it was plugged into, which lay on the floor beside the desk. Now, I was sure that switch was on when I left it. I could only think that Roomba must have rolled over it in its search for the way out, and pushed the switch off.
Someone suggested that it was trying to phone home for help!