TR/9 trip mine

The TR/9 Antipersonnel Mine, otherwise known as the Trip Mine or Mine, is a UNSC Equipment item usable in Halo 3.

Overview
The Trip Mine can be detonated by weapons fire or the close proximity or impact of a vehicle or infantryman; it does not use a remote trigger, however. The mine will explode after ninety seconds if not detonated before then. It is apparently capable of detecting the anti-gravity generators found on Covenant vehicles. It will not detonate, however, if a player crouch-walks over it. The technology it uses to detect nearby objects may be similar in nature to that of the Motion Tracker, which also fails to detect stationary vehicles and slow, crouched players.

Once deployed, it can be identified by a high-pitched beeping noise, four inner spokes that rise up, and a distinctive flashing bright orange light on its top. Its blast radius is considerably larger than a grenade or rocket explosion, throwing vehicles and personnel into the air. Despite this blast radius, however, Trip Mines can only slightly injure Spartans and Elites positioned near the edge of the blast radius, and it takes two direct hits with a Trip Mine to kill a Spartan or Elite. It will, however, kill Brutes, Grunts and unwary Marines, even if they are on the edge of the blast. The greater damage to Brutes may be due to the fact that their armor is weaker than the Mark VI and Elite shielding.

The Trip Mine spawns by default on Sandtrap, Rat's Nest, and Avalanche. Jump Pack Brutes have been seen deploying the mines against nearby players in Tsavo Highway. Destroying a vehicle with the Trip Mine in Campaign or Matchmaking will unlock the We're In For Some Chop achievement.

Tactics

 * The most important thing to note when deploying a Trip Mine is to inform your allies. Unwary teammates may activate your Mine, resulting in a betrayal.
 * In Campaign, you should destroy activated trip mines as you leave an area, as marines are scripted to run certain paths, and if an un-detonated trip mine is in the way, they may simply walk over it, killing as many as three or four of them.
 * When fleeing an enemy vehicle, it may be wise to deploy a Trip Mine in its path. Such a move may kill the occupants of the vehicle, though it also poses a risk to the player trying to flee.
 * A Trip Mine is a useful counter to a Bubble Shield. Throwing a mine into an occupied Bubble Shield will almost always result in its detonation, and the resulting blast will be contained within the shield, killing only its occupants. If the explosion destroys the shield generator, however, it may "escape" the shield.
 * If you deploy a Trip Mine on top of a Man Cannon, the mine will go flying out into the battlefield. In the Halo 3 Beta, the Trip Mine would sometimes disappear entirely when thrown into the Man Cannon. It would still explode if someone or something goes within the activation radius.
 * One of the most evil tricks, as Bungie has mentioned, is to deploy a mine in the exact position where it spawns. Some players will notice that the mine is armed, but many players will attempt to collect it, resulting in a kill (if the player's shield is almost depleted) which would certainly not have happened if the player was attentive. This tactic can easily result in a betrayal, however, so teammates should be warned.
 * Trip Mines can be used to block doors, hallways, sniper perches, and other areas.
 * If a player walks slow enough or crouch-walks over a Trip Mine, it will not explode.
 * A Trip Mine's beeping tends to reveal its presence, but by hiding it around a corner or over a ledge, a player can prevent the mine's orange glow from compounding the problem.
 * Throwing a Trip Mine underneath a vehicle will mask its glow, muffle its beeping, and turn the vehicle into a deathtrap.
 * In Capture the Flag, a player can place a Trip Mine by their own flag. It will kill any opponents that are trying to steal the flag. This tactic works very well when one flag gets the win; a good deal of players will be focused on getting the flag, so the Trip Mine would be ignored until it detonates.
 * In multiplayer, Banshees are commonly used to splatter enemies. If you happen to see a Banshee angling toward you and boosting, drop a Trip Mine. The explosion will probably kill both of you, but is usually still desirable, as Banshees are often hard to kill.
 * On Avalanche, slip a trip mine under the most valuable vehicle at the enemy base, since they know it is underneath one of the vehicles, they will most likely take the Scorpion, Wraith or Hornet, resulting in severe damage or death.
 * If a player has low shields and an enemy is chasing him/her, a good tactic is to throw the Trip Mine down. If the attacker comes around the corner, the resulting explosion will deplete their shields, allowing the defender to finish them off with a headshot. If the attacker hears the beeping and stays back, the defender will have a chance for their shields to recharge.
 * If two players are in close combat and one is about to die, the losing player can deploy a Trip Mine right at the other player, as an act of vengeful suicide.
 * Try making Trip Mines land upside down by bouncing off a wall or solid object, because they are much harder to see, since the light is pointed into the floor/ground.

Disadvantages

 * Sometimes, while playing in Multiplayer or Campaign, players can either accidentally run or drive over their own Trip Mines or those of their teammate(s).
 * A Trip Mine's distinctive beeping and orange glow makes it easy to detect.
 * The Trip Mine will only stay active for 90 seconds before spontaneously exploding.
 * Trip Mines can be detonated from a distance by weapons fire, and are therefore only useful when unnoticed.
 * The Trip Mine is often difficult to use in split-screen local games due to the sound it makes when deployed, causing other players to screenwatch.

Trivia

 * Even though it's said that this is UNSC equipment, Jump Pack Brutes always have one ready to use and no Marine or ODST has been seen holding one, though there are several Mines in a Marine base on Tsavo Highway.
 * It was hypothesized that the Trip Mine may be the book-aforementioned Lotus Anti Tank Mine or they may be both made by the same manufacturer. However, it is unlikely the Trip Mine is the Lotus Anti-Tank Mine, because a Scorpion Tank can easily drive over a Trip Mine and survive the explosion. It is possible that the Trip Mine is the Antlion Anti-Personnel Mine due to its similar operation.
 * The Trip Mine's HUD icon, along with that of the Bubble Shield, can be used in a Halo 3 Emblem.
 * Trip mines can be used to overload a map or launch an Elephant.
 * During the initial unveiling of Halo 3, a Bungie employee claimed that, "The Trip Mine is probably going to be used as a 'I got you' weapon as people only seem to drop it right before being splattered."
 * In the Halo 3 Beta, deployed Trip Mines could stick to the bottom of a motionless vehicle. If the vehicle then moved, the Trip Mine would explode, killing all players inside of it The Trip Mines in the beta were also more powerful.
 * If you set it off, while looking down at it you will see your body split in half for a moment.
 * The shape of the Trip Mine resembles the German made Tellermine series of anti-tank mines developed and used during the Second World War; both mines are hand carried to their targets and are sometimes tossed into the way of an enemy tank in hopes of destroying it.