The Joker has often used joy buzzers amongst his many, many weapons. Unlike a real-life joy buzzer, which merely creates a vibration that feels like an electric shock, the ones utilized by The Joker contain actual electricity, and are often used to electrocute unsuspecting opponents.
Most commonly, The Joker utilizes his lethal buzzers like a real prankster would: by offering his victim a friendly handshake. Once he clasps hands with his victim, The Joker needs only to squeeze to release the current, and hang on tight for a few seconds for the current to stop the victim's heart.
On several other occasions, The Joker has directly attacked opponents with the buzzer, not bothering to offer a handshake and simply clamping his hand down on their face or neck.
On very rare occasions, the "buzzer" will not be electrically-charged at all, but a simple needle-like device often tipped with Joker Venom.
The buzzer's charge is very often lethal to the victim, being able to stop their heartbeat within seconds. Oftentimes, the heat generated from the buzzer's electricity will "fry" the victim into a charred corpse.
In the rare cases where the buzzer is not (immediately) lethal, The Joker has been seen using it to knock opponents unconscious, or simply to induce large amounts of pain.
A "prototype" version of the buzzer first appeared in the 1940/41 story "The Cross-Country Crimes!", where The Joker, on the run from both Batman & Robin and the FBI, set up a dummy of himself to fool his pursuers. The dummy, when touched, would immediately emit a powerful electric shock that would knock unconscious whoever touched it. 
The Joker's first actual usage of a joy buzzer, ironically enough, would be with a real-life, harmless version. The buzzer was amongst the many gadgets in his self-built utility belt, and was used to distract a policeman so that he and his gang could overpower them and escape. 
1966 Television SeriesEdit
The joy buzzer was amongst the Cesar Romero-portrayed Joker's many gadgets in the campy, live-action 1966 Batman television series. In the third-season episode "The Funny Feline Felonies", he summed up its name and effects as such:
"It's my lethal Joker Buzzer. One by one, your five senses will leave you. Then your lungs will collapse. Then you'll be KAPUT. FINI. DEFUNCT!"
In the 1989 Batman film, The Joker, as portrayed by Jack Nicholson, utilizes a lethal electric buzzer to murder mob boss Antoine Rotelli and demonstrate to Gotham's other mob bosses what happens to those that cross him. The buzzer's effects are shown in gruesome detail, burning the flesh off of Rotelli's face and turning him into a smoking, charred skeleton.
Like in many other cases, Joker activates the buzzer by offering Rotelli a "friendly" handshake.
Aside from this scene, the buzzer makes no other appearances in the film.
Much like his comics counterpart, the DCAU Joker's first usage of a joy buzzer (in the Batman: The Animated Series episode "Be A Clown") is a harmless one. While masquerading as a clown for Jordan Hill's birthday party, The Joker utilized a harmless joy buzzer handshake on Jordan's father, Mayor Hamilton Hill.
The buzzer played a crucial role in the direct-to-video movie Batman Beyond: Return of the Joker, where Terry McGinnis uses it to destroy the microchip on the neck of Tim Drake. With the microchip destroyed, The Joker's genetic makeup was exorcised from Tim's body, and the Harlequin of Hate's ghost was finally laid to rest.
As the Joker was not allowed to murder onscreen by FOX executives, the buzzer was shown to cause intense pain and/or knock people unconscious rather than slaying them on the spot.