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The Rollermine is an electrically charged, spherical device, with morphed pentagons each side, slightly larger than a soccer ball that reacts to movement within a sizable radius. They are primarily used as offensive and defensive traps by the Combine, but reprogrammed by the Resistance, and Alyx Vance.


Rollermine duel

A reprogrammed Rollermine exchanges jolts with an unaltered one in the Citadel.

As the name implies, Rollermines roll towards enemies and electrocute them via close-range electric shocks. Extensively used along the coastal roads, they are deployed from the air by Combine Dropships, in groups of two to four. Upon landing, the mines will remain inert or, if they land on softer terrain like soil or gravel, they will burrow themselves into the ground, remaining almost invisible. When an enemy target is detected, the Rollermine will pop out of hiding and roll towards it in a relatively straight line.

The mines can magnetically cling to a target vehicle (such as the Buggy) and interfere with the steering, forcing the driver to either stop or drive off the road. Besides the damage inflicted by any resulting car wreck, attached Rollermines do not directly injure the occupants of a vehicle. For this reason, Rollermines are usually deployed in tandem with Combine soldiers, who ambush the stranded individuals. Attached mines cannot be removed except through excessive force, chiefly the Gravity Gun; touching them will merely cause electrocution. They are also deployed in buildings and structures, taking any intruder by surprise. Rollermines can be destroyed with explosive devices, or alternatively may be picked up with the Gravity Gun and launched out of the way (or at enemies). Complete submersion in water also causes them to short-circuit and explode. Additionally, one can elude Rollermines by outrunning them, as they cease chasing once a target is too far away. If Rollermines are caught in an explosion, they bounce up and detonate.

Alyx was at one point able to capture and disarm a Rollermine, which she then gave to her "pet dog" to play with, calling it a ball. Alyx had Dog use the "ball" to play catch with Gordon Freeman, so he could get some practice using the Gravity Gun.

In Episode One, Alyx reveals that she can use her Electro-Magnetic Pulse tool to temporarily reprogram a Rollermine's targeting system, making it friendly. Once reprogrammed, Rollermines will emit an orange light instead of their signature blue (by the Combine) and will follow the player slowly, attacking any Combine units it sees (including other Rollermines). Reprogramming Rollermines makes them unstable however, and they will invariably glow red and explode a few minutes later.

Behind the scenes

The Rollermine model seen in the Beta leak looked significantly different, bearing a huge resemblance to a sea mine (without the trigger points) and was more aggressive; attacking the target constantly, where as in the retail version when it attacks it has to charge before attacking again.


  • Rollermines can attach to the Scout Car and shock it - strangely, so will Dog's ball as if it was still active.
  • Rollermines can also be destroyed by placing them in a fire.
  • There is a glitch when the player picks up a Rollermine with a Dark Energy Gravity Gun (remember: it can only be acquired from using cheats to get the Dark Energy Gravity Gun), that causes the Rollermine to duplicate (duplicate Rollermines don't work and have no collision), as well as not being able to pick up the Rollermine. The same glitch with the Dark Energy Gravity Gun also occurs with Sentry Guns and Vortigaunts. However, the engine may become unstable and there is also a chance the game will crash.
  • There is another glitch involving Rollermines. If the player picks up a Rollermine with the Gravity Gun and launch it into the path of a Barnacle or Poison Zombie, it causes the entire engine to crash. Valve have stated that it is impossible to do this without use of cheats or mods, so they will make no attempt to fix it. However, this is possible to do in the unmodified game with Dog's ball in the mines after Ravenholm without the use of cheats.
  • Reprogrammed Rollermines seem to do varying damage to different targets. They can take out Overwatch Soldiers (50 HP) in two hits, and take out an Overwatch Sniper (125 HP) in one hit.
  • In Half-Life 2: Episode One during the scene where the sniper is first seen, even if the player only lets Alyx reprogram one Rollermine or player kills the sniper with the grenade, all of the Rollermines in the area will explode once the sniper is killed as if the other Rollermine is reprogrammed.

Dog's Ball

  • It is possible to take Dog's ball or active Rollermines through Ravenholm to Nova Prospekt, but invisible walls and glitches that have to do with friendly NPCs attacking it make it a very tough feat. There are also environmental challenges such as the other Rollermines, and having to go underwater, which will destroy Dog's ball if it is submerged too deeply. The upside of keeping the ball is that it is easy to kill Antlion Guards and hostile Antlions, Zombies, and individual Headcrabs. It also proves as a great distraction for Overwatch soldiers by holding it with the gravity gun, and can also be used as a shield or a projectile. It is also possible with Manhacks.
  • A useful technique is to take Dog's ball into Ravenholm with you as it will draw the Zombie's fire and allow an easier kill with less risk of taking damage.
  • If Dog's ball is taken through Ravenholm and through the mines there will be an invisible wall blocking the way to Shorepoint which will prohibit the Rollermine's entry to Shorepoint. However, if launched with the Gravity Gun high enough, it will go over the wall and the player will be able to enter the base and the later chapters. This tactic can be repeated for the three or more invisible walls later on. At the end of Sandtraps, the Rollermine can be placed outside the entrance. This will cause the ceiling to crumble, blocking the player from coming in but will allow the Rollermine (deactivated or active) to enter, despite it the debris.
  • Dog's ball will react to the G-man's presence outside Shorepoint but will do relatively nothing but follow him.
  • Dog's ball can kill Headcrabs by bumping into them repeatedly.
  • If one can get Dog's ball to New Little Odessa and place it in front of the Vortigaunt under one of the tables, he will randomly say all of their quotes for when he is done charging Gordon's suit.
  • Dog's ball has a hostile relation to the player and everything that's not allied with Combine Forces, it cannot shock anyone but will always chase enemies.
  • Despite Dog's ball being disarmed, one can still be harmed should the player bump into it while it's rolling at a high enough speed.
  • Bringing Dog's ball into Ravenholm is quite useful when players want to get the achievement "Zombie Chopper".


List of appearances


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