Rollermine

First Seen: Half-Life 2, Chapter Five, Black Mesa East - found as Dog's ball (inert); Half-Life 2, Chapter Seven: Highway 17 (active).
 * Health total: N/A
 * Weapon damage: Shock (10)
 * Entity:

Rollermines are electrically charged, spherical devices slightly larger than soccer balls that react to movement within a sizable radius. Rollermines are used as offensive and defensive traps by the Combine. As the name implies, they roll towards enemies in an attempt to electrocute them. Extensively used along the coastal roads, the mines 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. They inflict damage to people via close-range electric shocks.

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 shock the occupants of a vehicle, concentrating instead on shocking the vehicle itself. For this reason, rollermines are usually deployed in tandem with Combine soldiers, who would ambush the stranded individuals. Attached mines cannot be removed except through excessive force, and touching them will 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, they can be eluded by being outrun, as they give up once a target is too far away.

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 through much of Ravenholm. In doing so, the ball can be used to distract the many zombies there, 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). Dog's ball is destroyed if it is caught in any nearby explosions.

As of Episode One, rollermines can be reprogrammed by Alyx to be "friendly", if the player picks one up with the gravity gun and holds it in front of her. Once reprogrammed, rollermines will emit an orange light instead of their signature blue, will follow the player slowly, as well as being unstable (it will blow up after some time). If thrown into a room full of enemies, the reprogrammed Rollermine will follow the enemies and attempt to kill them. Whilst the game states that these co-opted rollermines only last a certain period of the time before self-destructing, it seems that these rollermines remain active until their scripted task (destroying a group of soldiers, for example) is complete, at which time the Rollermine will emit a red light and self destruct.

Some fans have noted the rollermines have a resemblance to a katamari from the Katamari Damacy video game series.