The voltaic bomb is Syndicate's stun grenade: a metal, plum-shaped device that releases an electric blast and drops nearby enemies. Alexander Graham Bell invents it, and you unlock it through the story memory Breaking News.
Bell builds the bomb to fend off Blighters sent by Crawford Starrick. He has three formulas and no time to test them, so the twins throw each from the rooftop while Bell stalls the thugs below, using fruit names as signals. The pear and apple versions only make a stink; the plum one knocks the gang out.
It is meant to incapacitate, but the voltage can still kill. Throw it into a crowd to stun several Blighters at once before you move in.
Fear Bomb
Fear bombs are a Jack the Ripper expansion tool: hallucinogenic grenades that scream on impact and send most enemies running in terror. Evie learned them from the Indian Brotherhood, and they let you clear a group without killing anyone.
Hallucinogenic Darts
Hallucinogenic darts fire silently from the twins' gauntlets and drive the target into a frenzy. Shoot one into a fire or other heat source and it bursts, spreading the toxin over everyone nearby. Bell builds the launcher after the twins intercept a recipe for the serum in Cable News.
Smoke Bomb
Smoke bombs throw up a cloud thick enough to blind and choke anyone inside it, giving you time to escape a fight, slip past guards or close in for a kill. They are part of Jacob and Evie's kit from the start and stay useful all game.
Spikes
Spikes are two-pronged hand weapons from the Jack the Ripper expansion. Evie uses them to pin an enemy to the ground, where a hallucinogen in the spike makes him scream in terror and spreads fear to the enemies around him.