Segway PT x2 Reference Manual page 54

WARNING!
To prevent a riderless Segway PT from traveling on its own,
never let go of it while it is in Balance Mode. It will travel some
distance on its own before shutting down, risking injury to
others and damage to the Segway PT.
WARNING!
Never place anything on the Mats, except your feet. Doing so
could interfere with the Rider Detect Sensors and allow the
Segway PT to travel on its own, risking running into a person
or property, and causing injury or damage.
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