Meet the Police Force Expandable Tonfa Baton: a tool designed to help you keep aggressive attackers at bay. It has a compact design and expands to 21″ at that flick of a wrist. The baton is made of aircraft aluminum and weighs only 1.25lbs.
This expandable baton has a rubberized handle to give you a firm grip. Not too expensive either.
[where to find it]