Type-1 Antipersonnel grenade

The Covenant Type-1 Antipersonnel Grenade, also known as the Plasma Grenade or the Sticky Grenade, is similar to the UNSC Fragmentation Grenade in that it is a thrown anti-infantry and anti-vehicle weapon.

Overview
The Plasma Grenade is a specially designed type of explosive (grenade) that sticks to its targets. Once it has made contact with a target, the plasma grenade will immediately bond to it, making any efforts of removal futile. The bonding mechanism holds its attraction until detonation, making it impossible to avoid its deadly explosion. Although it will bond to any target it hits, if it attaches to a piece of armor or a weapon, removing said articles will allow one to distance themselves from the explosion.

The "sticking" mechanism is complex enough to allow the plasma grenade the ability to distinguish between targets and inanimate objects. For example, it will stick to a soldier or a vehicle, but not a tree or a wall. This does not, however, allow the grenade to act selectively. The plasma grenade will not distinguish between friend or foe so accuracy and caution is strongly advised when throwing it.

The plasma grenade possesses a timer. It has a three-second fuse that counts down at the point of activation. A manual activation via a small button or a stimulated activation, such as another explosion or gunfire, will set the detonator and start the countdown. Delayed activation can also set the detonator after it either sticks to a target or otherwise comes to a rest. It is possible to tell if the grenade has been activated. A densely small and bright cloud of plasma emission will leak around the grenade as the explosive reaction takes place inside. This cloud will gradually grow to a larger diameter after each second of the countdown. A low sound is emitted by the grenade when activated, followed by two rapid beeps and a high-pitched whine just nanoseconds before the explosion. This is the plasma grenade's standard process of detonation. The Plasma Grenade appears to have two settings: the standard three-second fuse and a delayed manual detonation. The latter is seen in Halo 3 by suicidal Grunts hoping to ensure their enemy's death by exploding right next to them.

Advantages
Sticking an enemy with the plasma grenade will always kill them when it detonates, no matter what. Even a fully shielded Spartan or Elite (with the exception of higher-ranking Elites like Ultras on higher difficulty levels) cannot withstand a stuck plasma grenade. The plasma grenade is slightly more powerful than the UNSC fragmentation grenade. If it goes off at the base of the target's feet without bonding it still results in a kill. A player wearing a fully charged Overshield may be capable of surviving the blast even when stuck.

Disadvantages
The plasma grenade's bright blue glow and longer delay fuse allows enemies to easily notice and avoid it. It can not be used around corners well, as it does not bounce, nor does it roll. Also, if a smart enemy is stuck when they are too close they can simply run toward you to catch you in the detonation. In Halo 2 and Halo 3, a primed plasma grenade in flight can be detonated mid-air by another explosion. Weapons capable of this include the Rocket Launcher, Brute Shot, Missile Pod, Frag Grenades, other Plasma Grenades. The Plasma Grenade will not stick to certain types of armour such as that of a scarab or a Brute Chieftain's. When thrown at them, the grenade will fall to their feet, most likely to have noticed it beforehand. Ballistic or explosive weapons fire such as a shotgun or brute shot will remove the plating allowing the grenade to stick.

Story
It has been shown that prolonged exposure to the radiation emitted by plasma grenades can cause a deviation in the neural electric pathways of the user--a disorder called Boren's Syndrome. This disease can be fatal if the person does not get treatment.

Stickiness Theory
Note: The following is speculation and is not considered canon.

The plasma grenade may stick by producing a thin layer of plasma which, when in contact with a target, fuses to the target. The reason the plasma grenade sticks to vehicles and characters may be due to an ability to sense heat. Body heat and the heat from vehicles engines is most likely what causes it to stick. Since a "dead" wall doesn't emit heat, it will however stick to the "living" walls of a Flood Hive.

It is also theorized that there is a complex internal mechanism built into the grenade that gives it this characteristic. A gravity generator may be built into the core of the device, giving it its own force of attraction. This artificial force of attraction is highly concentrated, which is exactly why the grenade is impossible to remove.

a thied theory is that the greanade might fuse with the natuaral plasma in a persons bloodstream.the reoson it sticks to vehicles is because that traces of plasma might be somewhere on there or that the plasma can sense a person through the metal.

Trivia

 * In Multiplayer, if you stick an enemy with the plasma grenade you are awarded with the Grenade Stick Medal.
 * In Halo 2, when the Covenant use plasma grenades in battle, they will shout phrases as they throw them, such as "cleansing flame", "flare" and "holy light". This is similar to their belief of Halo.
 * If John-117 throws a plasma grenade, the Covenant will call it a "demon flare". However, when the Arbiter throws a plasma grenade, Elites and Grunts will still address it as a demon flare, even if the grenade is a frag. This may prove that all kinds of enemy grenades are demon flares. This may be as a kind of slang, with "demon" referring to the enemy, or enemy thrown grenades, and holy in the opposite manner.
 * Often times, when an NPC is stuck, they will have some type of reaction to being stuck.
 * Occasionally, if two plasma grenades are thrown in succession at the same spot; one will detonate, launching the other into the air. The airborne grenade will explode in mid-air, causing a "fireworks" effect. This was easier to perform in Halo: Combat Evolved.
 * If you stick a charging Hunter with a plasma grenade the Hunter will instantly turn around, exposing its back, when the grenade explodes.
 * In Halo:CE, if you throw a Frag grenade where a group of plasma grenades are, the detonation of the frag will make the plasma grenades explode.
 * In Halo:CE, Plasma Grenades take 4 seconds to detonate. In Halo 2, they take 3 seconds. In Halo 3, they take about 2 and 1/2 seconds.
 * On one side of the Plasma Grenade, a Forerunner Symbol is visible.