As I recall, as a past Dealer, a Segway knows whether or not there are no feet, 1 foot or both feet.
It makes appropriate decisions.
No feet = nobody aboard.
2 feet = normal operation
1 foot = interesting.
If you are cornering and it sees a transitions from 2 to 1, then it assumes you are near the boundary of rider control, and eases the steering, but continues to run.
I think that if there's only 1 foot, max speed is reduced.
Interesting stuff like that.
Season's Greetings
Michael
www.dgbint.com