Tasers
(Info)
In 1x05 - The Tell, Kate Argent uses an electrified baton as a taser, to knock Derek down. She claims the baton produces 900,000 volts.
The shock makes him shift back to human and largely incapacitates him. He writhes in pain, cannot stand, and can barely speak. It only takes a few minutes for him to recover enough from the shock to be able to run, however, so the effects are shortlived.