They can see you but you can't see them, They can see where you were while you could not see where were them, they will see you but you may see them. Gas poisoner spy (GPS) are mysterious mercenaries who are often working for mysterious bosses, they kind of work as ghost, creature that you cannot see. Those sneaky minions are sneaky thanks to their developped sneak skills which make people call them "ghosts of the streets", Don't forget that they are human despite their low profile.

Their name "Gas poisoner" is in reason of their regular uses of gas, but here comes the language mistake, because they Don't use mortal gas.