From Wikipedia:
A Taser fires two small dart-like electrodes, connected to the main unit by conductive wire and propelled by small compressed nitrogen charges similar to some air gun or paintball marker propellants. The air cartridge contains a pair of electrodes and propellant for a single shot and is replaced after each use. There are a number of cartridges designated by range, with the maximum at 35 feet (10.6 meters).[8] Cartridges available to non-law enforcement consumers are limited to 15 feet (4.5 meters).[9] The electrodes are pointed to penetrate clothing and barbed to prevent removal once in place. Earlier Taser models required the electrodes' barbs to penetrate the skin, but newer versions (X26, C2) use a "shaped pulse" that increases effectiveness in the presence of barriersEarly models had difficulty in penetrating thick clothing, but the 'pulse' models are designed to bring down a subject wearing up to a Level III body armor vest.
Some Taser models, particularly those used by police departments, also have a "Drive Stun" capability, where the Taser is held against the target without firing the projectiles, and is intended to cause pain without incapacitating the target. Taser defines "Drive Stun" as "the process of using the EMD weapon [Taser] as a pain compliance technique. This is done by activating the EMD and placing it against an individual’s body. This can be done without an air cartridge in place or after an air cartridge has been deployed."

A Las Vegas police document says "The Drive Stun causes significant localized pain in the area touched by the Taser, but does not have a significant effect on the central nervous system. The Drive Stun does not incapacitate a subject but may assist in taking a subject into custody."[10] "Drive Stun" was used in the UCLA Taser incident and the University of Florida Taser incident.

It is also known as "dry tasing", "contact tasing", or "drive tasing
It sounds like they use the 'Drive stun' is less likely to produce an unintended death, but not as effective on a totally whacked-out suspect as it produces pain and not the full stun effect.