My only previous definition for "monadnock" was Mount Monadnock in southern New Hampshire.
A monadnock is a prominent hill sitting above a plain, and its granite resisted it being ground down by glacial till, so it stands by itself without hills nearby.
In this case,Monadnock is the maker of a police baton known as model PR-24. The joke is that the PR stands for "Public Relations", and it's 24" long.
Tonight at Academy, I looked over a Smith and Wesson collapsible baton, 16" when fully extended. It comes with a belt holster which will hold it fully retracted. The price was $39.99 and they had several in stock.
The link above allows you to shop for higher end batons, which are priced 3x to 4x the price of the Smith and Wesson. I expect that they must be quite stong, in order to justify their higher price.