The Scout Guard is a robot, usually stationary or often following a set track, only breaking from this track if it spots and enemy of the nation it guards, you will not find it in Stones Ruin if you are an undecided player, as you have not chosen a side, you technically have no current enemy nation. Scout Guards often become more difficult to take down and deliver bigger blows to your armor the closer you get to central locations belonging to the other nation, for example, a Scout Guard in Starlite Valley will not hurt an ANI player as much as one in the Bach Mountain Chain, it will also be easier to take down.
Scout guards are present in Safe Zones as well, why this is so, that is unclear, however, they are more plentiful in Battle Zones, as these are the only maps belonging to one nation that the other can infiltrate through a series of warps.
Scout Guards can vary in appearance depending on your location due to Episode and nation variants, they can look like small, cycloptic robots with several thrusters and a small gun located at the bottom, or appear as a floating machine gun, or potentially a 4-limbed, odd looking, gun weilding robot.
Scout Guards will not attack those of their own nation, nor can they be damaged by those belonging to the nation it protects, you cannot target it, you cannot shoot at it, and it will ignore your existence entirely.
Although single hits can be damaging to some mid-level gears not equipped for damage, they are easy to escape from, if they do leave their post, they are very slow, and can be escaped easily, numerous Scout Guards in a concentrated area as you are warping into said concentrated area however, can provide sufficient damage to some.
Scout Guards will not kill monsters, and since they never come in contact with other Scout Guards from the opposing nation, it is unknown if they would kill eachother hypothetically. You can target and destroy enemy nation Scout Guards. It may be difficult for some, and easy for others.