Rollermine

The Rollermine is an electrically charged, spherical device slightly larger than a soccer ball that reacts to movement within a sizable radius.

Overview


Rollermines are used as offensive and defensive traps by the Combine. As the name implies, they 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 roller mine will pop out of hiding and roll towards it in a relatively straight line.

The mines can magnetically cling to a target vehicle 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.

Take note that Dog uses an inert rollermine as the ball during the game of fetch Gordon plays with him in the Black Mesa East scrapyard. If Dog's ball is not destroyed during the shelling of Black Mesa East, it is possible to carry it with the gravity gun all the way to the end of Nova Prospekt, though it needs to be thrown over a number of invisible walls along the way. In doing so, the ball can be used to distract zombies and antlions, who will attack it instead of Gordon, making them easy targets (The rollermine can also "run over" most basic forms of headcrab, thus killing them).

In Episode One, Alyx reveals that she can use her EMP tool to reprogram a rollermine's targeting system, making it "friendly". Once reprogrammed, rollermines will emit an orange light instead of their signature blue 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 emit red light and explode a few minutes later.

Behind the scenes
The rollermine model seen in the Beta leak looked significantly different, bearing some resemblance to a sea mine and was more aggressive such as attacking the target constantly as the final version when it attacks it has to charge before attacking again.

Trivia

 * There is a glitch, that when the player picks up a rollermine with a Dark Energy Gravity Gun (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 turrets.
 * 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, it causes the game 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.

List of appearances

 * Half-Life 2 
 * Half-Life 2: Episode One