The S5LM Guardian, identified as Guardian when targeted, is a Core Dynamics remote-control Skimmer commonly used for security operations at high-security Settlements. It is assigned to patrol a specific area and use its weaponry, which includes High-Explosive Seeker Missiles, to defend against intruders. The Seeker missiles detonate at close proximity rather than at impact. They appear as blinking triangles on the SRV's radar, and can be individually targeted and shot down.
Core Dynamics S5LM 'guardian' skimmer – Based on their S4 skimmers but with reduced weight, and with an enhanced missile launcher weapon mount. A more expensive solution, but often used to protect higher value installations. It sacrifices armour to carry the weight of missiles and so is more vulnerable.
— Newsletter #94
The S5LM Guardian is far more fragile than the S4 Sentry, but is capable of dealing serious damage whilst engaging from its maximum range (~550 meters) where it can be much harder to shoot back at; all the Guardian has to do is pop up, lock onto its intended target, fire its missiles, and duck back behind shelter. Sentries, by comparison, can lay down suppressing fire at such ranges, but won't hit very often and don't do very much damage even when they do hit.