A portable transporter was a portable site-to-site transporter device which allows beaming from one location to another without using an external transporter pad or system. While the devices could be carried along, some were known to be rather large and bulky. Some portable transporters had the ability to transport themselves along with the payload.
In 2371, Commander Benjamin Sisko theorized that Morka, Atul, and Bo'rak used a portable transporter to place a piece of surveillance equipment in a bulkhead. However, Constable Odo did not believe the Klingon Intelligence personnel would be seen walking through Deep Space 9's corridors with a large device such as a portable transporter. (DS9: "Visionary")
In an alternate timeline, Tom Paris had acquired a hand-held site-to-site transporter. He and Harry Kim used the device to transport from a San Francisco street to Harry's office at Starfleet Headquarters and from the office to the Earth Spacedock in 2372. This type of transporter beamed itself along with the transported personnel. (VOY: "Non Sequitur")
In 2375, the Borg drone One developed internal transporter nodes based on the 29th century mobile emitter technology. These implants could be utilized as a personal portable site-to-site transporter. (VOY: "Drone")
The emergency transport unit was a miniature portable transporter device developed in 2379. It was designed to provide a single one-direction transport for one individual. During the Battle of the Bassen Rift, Jean-Luc Picard beamed from the Scimitar to the USS Enterprise-E using such a device. (Star Trek Nemesis)