Power drain

The Power Drain is a short-range, tactical, energy sapping device which made its debut in Halo 3.

Function
The power drain creates a short-range Electromagnetic Pulse (EMP) effect which causes disastrous failure of powered field systems within a set radius, and is designed primarily to interfere with common varieties of electrical field-based shielding, vehicles and power generation. It also has a damaging effect on biological systems and can wound or kill most bipeds in its resulting explosion.

Essentially, the Power Drain is a reverse to the Regenerator; instead of energizing a player's shields, it causes any player's shields within the area of effect to drain away quickly, making them vulnerable to harm. The self-destruct explosion after the activation of the Power Drain will not kill you (If you were at full armor health previous to deploying it), but will take your health to critical levels. The Power Drain can also disable vehicles via EMP, rendering them unable to move (but the vehicle can still use and aim its weapons) when they drive or fly through it and even about five seconds afterward. If a Regenerator and Power Drain are deployed in close proximity, the Regenerator will continue to work, but its effect is overwhelmed by the Power Drain.

The Power Drain, like the Bubble Shield, Trip Mine, Radar Jammer and the Portable Gravity Lift, are all in the category of equipment and can be deployed using the default "X" Button. It activates shortly after it is thrown - just enough inactive time to travel away from the user, leaving them unaffected.

Tactics

 * This equipment will stall a vehicle's engine, but the weapon/weapons on the vehicle still work. The most effective way to take out an armored vehicle such as a Warthog is to throw a Power Drain followed by a grenade, killing most of the players on board. Several follow-up shots will take out any survivors.
 * This is a good piece of equipment that is well-used in conjunction with headshot-capable weapons such as the Battle Rifle, Carbine and Magnum.
 * This is the piece of equipment that is useful when outnumbered; once drained, the whole group of enemies becomes a big one-hit-kill target.
 * Bubble Shields cannot block the Power Drain from entering, so it's a good idea to throw one inside of a Bubble Shield while your enemies are inside of it.
 * If the Power Drain unit hits the Bubble Shield unit, the Bubble Shield may move, depending on how fast the Power Drain is going at the point of impact. This can sometimes rob your enemies of the shield's protection, making them incredibly easy targets and can lead to some rather degrading deaths. A particularly humiliating example of this tactic can be seen in a Top Ten Series episode.
 * Deploy this equipment near a popular sniper position or an area where people land after they get off of the Man Cannon, after that, it's another one-hit-kill target.
 * Try keeping some distance between you and your foe when in combat, as when in close quarters battle, they tend to use power drains.
 * The Power Drain is a great way of 'jacking' an enemy's vehicle. For example, you can throw one at a Warthog or Wraith, and then when they're low on energy shields, hijack their vehicle and it will most likely kill them and gain you a vehicle. Also, if a Banshee is close to the ground, a Power Drain can force it down, then you can skyjack their vehicle.

Trivia

 * The Power Drain lasts approximately 6.5 seconds, with 0.5 seconds rendered inactive while throwing, a total of 7 seconds.
 * The Power Drain, Radar Jammer, and Flare are all visually identical, save for the color of the glow each item emits.
 * The effects of the Power Drain can also pass through walls and floors so simply fleeing to the bottom floor after an enemy activates one may still strip your shields through the ceiling if you pass through it. This is most notable on levels such as Guardian.
 * The Power Drain can be used in a glitch called Equipment Jumping by moving you player against a wall, jumping, and then at highest point of the jump deploy the Power Drain and you will be able to jump off of it in mid air. This is a great tactic for reaching high areas of a map such as the second level of the tower on The Pit. This can also be done with the Radar Jammer and Flare, however, the Power Drain variation of the glitch can only be preformed as an Elite.
 * Strangely, in Halo 3: ODST when you are in the radius of a power drain your stamina will drain, even though it's not powered by anything at all. This is just for a gameplay reason, although there is research that seems to indicate that electromagnetic frequencies can effect one's sense of well-being, sometimes making them feel unusually tired.