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 is activated by proximity or impact of a vehicle or personnel. Once deployed, it can be identified by a high-pitched beeping noise, 4 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. The Trip Mine cannot be deactivated once deployed, but it will explode after about ninety seconds if it is not triggered. However, it can be remotely detonated by projectile weapons or grenade explosions. There is no device that can detonate the mine. The Trip Mine, while having a larger blast radius than a Frag Grenade, will only slightly injure a Spartan or Elite when they are positioned near the edge of the blast radius. It will, however, kill Brutes and unwary Marines, even if they are on the edge of the blast. The greater damage to Marines and Brutes may be due to the fact that they do not have Energy Shields. The fragments will slip through their armor and kill them.

The Trip Mine spawns by default on Sandtrap, Rat's Nest, and Avalanche. Destroying an enemy vehicle with the trip mine in Campaign or Multiplayer will unlock the We're In For Some Chop achievement. Brutes may sometimes deploy Trip Mines. In Multiplayer, a single Trip Mine is incapable of killing a player, it will only injure them. On foot, a player must have two or more mines available to kill someone with a full shield without the assistance of a weapon or grenade. This is impractical, because a player cannot carry multiple Trip Mines, and the player's victim will most likely avoid a second Trip Mine. It also will not destroy vehicles if they drive over the mine unless the driver is already weakened. Vehicles that use anti-gravity ( Ghosts and Wraiths) can also be damaged or destroyed by the mines. A vehicle that doesn't touch the mine, but gets close can cause it to detonate.

Also, in Multiplayer maps, trip mines can be used as part of a known glitch, commonly called overloading a map, to disable certain parts of a map, such as Gravity lifts, Mancannons, Sandtrap's minefield, and Snowbound's Automated Turrets.

Tactics

 * When running away from an enemy vehicle, a mine can be deployed in front of the approaching vehicle. This may kill the occupants of the vehicle, but it carries the risk of killing the player who deployed it.
 * Try to combine the powers of the trip mine with different pieces of equipment to make interesting effects. For example, its useful to drop a trip mine into an enemy Bubble Shield. The resulting blast will be contained within the Bubble Shield, killing your opponent but keeping the player who deployed it from receiving any damage in return.
 * If you deploy a Trip Mine on top of a Man Cannon, the mine will go flying out into the battle field. Throughout the 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 mentioned before is to deploy a mine in the exact position where it spawns. Some players will notice that the mine is armed (by listening to its distinct audio and visual cues), but most players will attempt to collect it, resulting in a kill which would certainly not have happened if the player is attentive. However, this tactic can kill teammates, it is wise to communicate with them beforehand.
 * Trip Mines are the only equipment currently in Multiplayer that can directly kill enemies.
 * Place Trip Mines in doorways or sniper perches, someone will step on it eventually.
 * Throwing a Fragmentation Grenade at a trip mine can cause extra damage.
 * If a player walks slow enough or crouch-walks over a trip mine, it will not explode. Although you are doomed if any enemy sees you doing this.
 * The Trip Mines glow and beeping sound gives it away (as mentioned in disadvantages), although, it can be placed on the one side of a hill, as an example, so the driver of a vehicle will still hear it, but not see it as they are passing from the other side. The Trip Mine will detonate when the vehicle passes over the hill.
 * Another tactic is to throw a Trip Mine under a vehicle, so it is harder to see and the sound is muffled. When a player moves while in the vehicle he or she will activate the trip mine. This works especially well on enemy aircraft.
 * In capture the flag, a player can place a Trip Mine by their own flag. It will kill any opponents trying to steal the flag. This tactic works very well when one flag gets the win. A good deal of players are focusing on getting the flag, so the mine would be ignored until it detonates.
 * In the level Tsavo Highway, Trip Mines are a useful way of destroying the Choppers by throwing it at the chopper once it starts charging at you. They are a one hit kill on lower difficulties, allowing players to unlock the "We're in for some Chop" achievement. To make this easier, a plasma pistol overload can be used to disable the Chopper. When it is stationary, a trip mine can be placed right in front of it, guaranteeing death for the enemy.
 * 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.
 * If a player has low shields and an enemy is chasing him/her, a good tactic is to throw the trip mine down. So when the enemy comes around the corner, it will explode, taking down his/her shields. He/She can then be finished off with a shot from a battle rifle. If the opponent hears the beeping and doesn't come around the corner, it gives the player chance for your his/her shields to recharge.
 * Always remember where you left your Trip Mines and tell your teammates as well to avoid betrayal

Disadvantages

 * Sometimes, while playing in Multiplayer or Campaign, you can either accidentally run or drive over your own self-activated Trip Mines or in co-op you can obliviously run over your teammate's Trip Mine. Without proper communication, you may also end up killing your own teammates with this device.
 * Be aware about where you are tossing the mine and don't forget it's location.
 * Players can be clever and use their enemy's Trip Mines against them by luring them into the blast radius.
 * It is easy for an enemy to see a Trip Mine that you have deployed due to it's glow, additionally it makes a distinct beeping noise.
 * While it could instantly destroy vehicles in the Beta, it now only takes down shields. However, for whatever reason, most riders in a vehicle will be killed by directly driving over a Trip Mine in the final version of Halo 3, even though their vehicle may suffer only minor damage.
 * The Trip Mine is fairly small, so vehicles could easily evade it.
 * The Trip Mine will only stay active for 60-120 seconds, so if you have a place wired with Trip Mines they might go off before another player steps on one.
 * Although powerful in the Halo 3 Beta, the Trip Mine was significantly reduced in power in the final release. Dispute and unrest about this change still continues on the Halo 3 forums.

Trivia

 * 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. 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.
 * The Trip Mine along with the Power Drain is the best equipment choice to get the achievement "We're in for some Chop", as it can easily destroy a Brute Chopper with appropriate effortlessness.
 * The Trip Mine logo, along with the Bubble Shield logo is a Halo 3 multiplayer emblem.
 * The Trip Mine was referred as a "Health Pack", though ironically to other players or "noobs".
 * Trip Mines can be used to overload a map, deactivating certain parts of the map, such as the Automated Plasma Turret in Snowbound, or the Brute Landmines in Sandtrap.
 * 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."
 * It's nearly impossible to kill Jackals with a Trip Mine because Jackals fight and move in crouching positions.
 * You can throw a mine down on an opponent and follow with a grenade or a headshot for a guaranteed kill with normal shields.
 * In Halo 3 Beta, Deployed Trip Mines could stick to the bottom of a motionless vehicle. If the vehicle then moves, the Trip Mine explodes, killing all players inside with normal shields.
 * Named the Trip mine because when a vehicle rides over it, the vehicle "trips" with a bang.
 * Even when jumping over it, it can go off.