The Hopper Mine is an anti-personnel proximity mine that hops into the air towards the target before exploding, much like a bouncing betty. These mines are carried and deployed by Shield Scanners. They are vaguely dome-shaped with three sharp "legs". When dropped, the mines use these legs to bounce around until they land facing up on a smooth surface. They then jam the legs into the ground, attaching themselves very firmly.
When an enemy target comes close, the mines light up and give off a warning chirp. If the enemy target gets too close, the mines will toss themselves nearly two meters (six feet) into the air in the direction of the threat and explode upon contact with whatever they happen to hit on the way down. They also detonate if smashed too violently. Otherwise, they are impervious to nearly all forms of handheld weaponry, save for the Gravity Gun.
Because of their danger, immovability and extreme durability, Hopper Mines are impossible for most enemies to disable or defuse. Thus, they are used by the Combine almost exclusively to deter attacking enemy personnel, creating makeshift but often impassable barriers in seconds. They are used both indoors and outdoors, mostly in vital choke-points and occasionally concealed as traps.
Hopper Mines use a friendly fire identification system which resets whenever they are picked up. The mines interpret a "friendly" unit as whichever faction placed it last. Thus, a mine placed by a Citizen with a Gravity Gun will attack Combine, and a mine dropped by a shield scanner will attack Citizens. This system is signaled through a color-coded light at the top of the device:
- Green: The mine is armed and considers whoever is close to it to be a friend.
- Red: The mine is armed and considers whoever is close to it to be an enemy.
- Blue: The mine is neutral and has not yet armed itself.
- Orange: The mine is in panic mode, having been rooted from the ground (with the Gravity Gun) and is uncontrollably attempting to re-grip the ground.
- No light: The mine has not yet been activated or the area does not contain any living things.
If thrown using the Gravity Gun's primary fire, the mine explodes on contact with whatever it hits first. Alternatively, as a last-chance effort, as a mine hops in the air it may be shot away using the Gravity Gun's primary fire. This is particularly useful if a mine remains unnoticed until after it has hopped. In addition, if the mine can be caught by the Gravity Gun before hitting something, it will not explode. The legs will flail in an attempt to jump, thinking it must still be grounded. After being dropped, the mine will reset itself and become friendly.
- In Half-Life 2: Episode Two, several mines are found in Resistance areas, and can be told apart from regular mines due to an orange "smiley face" or Lambda symbol painted on their underside as well as yellow paint coating on top. If you shoot them at near Alyx she'll make a movement to block her face.
- Sometimes the A.I. of the Hopper Mine has a hostile relationship to the Manhack.
- If the player fires the Hopper Mine into the air, then sends an ally to its estimated landing position, the explosion will hurt or kill the ally. Firing it directly at the ally, however, won't hurt the resistance member at all. This is because direct friendly fire will not hurt the ally, due to friendly fire being cut in the development of the game (this also applies to explosive barrels).
- Hopper Mines appear to be waterproof; they function normally when placed underwater.
- A skilled player can "launch" Hoppers by dropping them with the Gravity Gun, then punting it before it can lock onto the ground. This can allow the mines to be placed on higher ground.
- There is a glitch where the player can use Hopper Mines as a floating platform by picking them up with the gravity gun, finding a nearby wall, placing them, and allowing them to reposition themselves on the players head, then "attatching" to the air, floating.
- In Garry's Mod, the Hopper Mine is by default neutral to the player(s), therefore being close to one does not give a friendly or hostile light and does not jump when approached.
- The concept of the Hopper has been around since World War 2, the most notable being the German 'S-Mine' (A.K.A. 'Bouncing Betty') and the American M16 Mine.