The Fusion coil is the "safest, most intelligent way to transport and store highly explosive compressed plasma energy." The containers are made primarily out of glass and aluminum. There is high voltage and radioactivity stored in a Fusion coil. Formerly, there was speculation that the actual core was a highly volatile radioactive power source for ground operations by the UNSC, although this has been denied by Bungie.
Several shots from any weapon can detonate these volatile coils. The explosion is a bloom of yellow and red superheated gas and sparks.
In multiplayer, players often may attempt to lay an ambush for a hostile near a coil by tossing a Fragmentation Grenade towards the coil when the enemy forays near. Alternatively, they can be pushed from above onto passing enemies, exploding on impact with the ground, or used as anti-vehicle landmines at vehicle choke points. They have also been used for Explosive Jumping and in Forge to create perpetual explosions.
Fusion coils feature prominently in Forge, where players can place a large amount of coils on any location in a map and detonate them. A Bungie Weekly Update described an incident where a beta tester used them, along with the Instant Respawn trick, to turn an Elephant into a "satanic piñata".
Fusion coils appear in all of the maps in Forge, and if they kill a player, that player disintegrates as if they were hit by a Forerunner weapon. There is also a foreunner type Fusion coil in the campaign, on the level Forerunner.
Some people don't think much about using these coils as an effective strategy. However these coils are pretty good trap items on Forge. If you see a player near one, shoot the coil. It'll weaken the player or kill him, depending on the number of coils nearby. Note: If the coils are near you too, be careful. Blowing one up will blow up others, causing a chain reaction. If encountered in Campaign, stick to Multiplayer tactics for there's not much difference. Also in Forge, if you find a choke point, it is often a good idea you place fusion coils in it, then detonate them with a long-range weapon.
- A trap can be made by shooting one with a Shotgun at a certain distance, causing it to fall over and glow white before having a very delayed detonation, which also be triggered by touching the glowing container.
- Fusion coils can be used in Forge to flip Elephants and create perpetual explosions.
- Fusion coils were not used during the events of Halo: Combat Evolved.
- In the Halo 3 Manual, under "The Forge - Co-op" It references "Cooperate with your friends to make the work go faster, But don't forget to throw a Fusion Coil at them from time to time."
- Fusion coils cannot be damaged by overcharged plasma pistol shots, although they can with regular shots.
- The humming noise that Fusion coils make will become progressively louder and faster as they take more damage.
- In Halo: Reach, fusion coils negate all fall damage if landed upon.
- If placed on the ground in Forge they take normal damage but if placed on a wall or ceiling they only take one shot to destroy.
- Halo 2 (First appearance) (Multiplayer only)
- Halo 2: Anniversary (Multiplayer only)
- Halo 3
- Halo 3: ODST
- Halo: Reach
- Halo 4