A transporter small enough to be worn or carried by one person, commonplace by the 32nd century, where Starfleet builds the function into every officer's tricom badge.
By the 32nd century a transporter no longer needs a room, a pad or an operator. Individuals carry their own units and beam themselves from place to place at will.
The technology is introduced in the Discovery episode That Hope Is You, Part 1, in which the courier Cleveland Booker depends on a portable unit that must recharge between jumps, and Michael Burnham makes use of it during their escape from the Mercantile. From Die Trying onward, Discovery's crew receive Starfleet badges with the same ability, and site-to-site beaming around the ship becomes routine.
Personal transporters still exist in the period of Starfleet Academy, and jamming them is a standard way of trapping an enemy, as the cadets discover aboard the derelict Miyazaki in Come, Let's Away.