Stim plug

Stim plugs were small electronic devices used to awaken or revive patients. They were a standard device used by medical droids. They likely used a small electronic discharge as well as a dose of stimulant to revive patients.

Behind the Scenes
Oddly, the Stim plug used to revive Anakin Skywalker in Downfall of a Droid was placed on in robotic arm. Since the device was only described and named in the Decoded annotations for the episode, it is unclear if the animators originally intended for it to be a device that effected his biological or robotic parts.