TR/9 trip mine

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

Overview
The Trip Mine is activated by proximity or impact. Note that it is very effective against vehicles. Once deployed, it can be identified by a high-pitched beeping noise, 4 inner spokes that rise up and a distinctive flashing orange light on its top. It's blast radius is considerably larger than a grenade explosion or rocket explosion allowing vehicles to be thrown into the air. The Trip Mine can not be deactivated once deployed. It will explode after about ninety seconds if nothing triggers it. However, it can be remotely activated by projectile weapons or grenade explosions. The Trip Mine, while having a larger blast radius than a Frag Grenade, will only slightly injure a Spartan or Elite, when they stand on the fringes of the explosion. It will, however, kill Brutes and unwary Marines, even if they are on the edge of the blast. The Trip Mine only spawns by default on Sandtrap and Rat's Nest. Destroying an enemy vehicle with the TR/9 in Campaign or Multiplayer will unlock the Achievement We're In For Some Chop. Brutes may sometimes deploy Trip Mines. In multiplayer, one trip mine will not kill anyone in one hit as {stated before} will only injure them, unless stepped on. It will also not destroy vehicles if they drive over the mine unless the driver is already weakened. Unfortunately, on foot, you have to have two or more mines to really kill someone at full health. Be sure to have another means of finishing off your mine's victim

Tactics

 * When running away from a moving vehicle, a mine can be deployed in front of a moving enemy vehicle. Be careful though, it may kill not only the driver and passengers, but you as well.
 * Try to combine the powers of the trip mine with different pieces of equipment to make interesting effects. For example, its fun 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 you 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 were to go 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 a kill which would certainly not have happened if the player is attentive.
 * Trip Mines are the only equipment currently in multiplayer that can directly kill enemies.
 * Try throwing a frag at a trip mine for extra damage.
 * Another trick with the Trip Mine is if you crouch and walk over it, it will not explode.
 * The trip mine's 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, but not see it as they are passing from the other side, but they should still be able to detonate the trip mine when they pass 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 the player moves while in the vehicle he/she will activate the trip mine.
 * In capture the flag, try putting a trip mine next to your own flag, it will kill any oppents trying to steal the flag, works very when one flag gets the win. A good deal of players are focusing on getting the flag, the mine would be ignored till 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 one hit kill with the choppers and also merit the "We're in for some Chop" achievement.

Disadvantages

 * Sometimes, while playing in multiplayer or campaign, you can accidentally run or drive over your own trip mines. Without proper communication, you may also end up killing your own teammates with this device.
 * Players can be clever and use their enemy's trip mines against them by luring them into the blast radius.
 * Trip mines are ultra sensitive! When you move away after having placed the mine, don't go near it again.
 * It is easy for an enemy to see a Trip Mine that you have deployed due to it's glow, additionally It makes a loud beeping noise

Trivia

 * It was hypothesized that the Trip Mine may be the Lotus Anti Tank Mine, or they may be both made by the same manufacturer. This is unlikely, though, as a Scorpion Tank can easily drive over a Trip Mine and survive.
 * The Trip Mine is the best equipment choice to get the achievement "We're in for some Chop", as it can easily destroy a chopper.
 * 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" ironically.
 * Trip Mines can be used to overload maps so you can go outside the boundaries of the map.