How did the Paladins catch Jumpers before the discovery of electricity?

The 3rd book: Jumper: Griffin's Story, reviewed here, released just before the film, incorporates more of the film's elements, most notably the Paladins (who weren't in the first 2 books).

This reveals that some Paladins can sense Jumpers if they're nearby when they jump.
In medieval times when towns, villages and populations were a lot smaller and without modern technology, this ability would have been crucial.