Informers were Grineer surveillance drones exclusive to the Informant Event. Players were tasked to locate and destroy any Informers they would encounter during a Grineer mission. Although they were stationary and could not attack, Informers were equipped with Orokin cloaking technology which would activate upon the slightest amount of damage, be it from players or the Grineer. Thus, players had to destroy Informers in one shot to make sure they did not escape. Informers were removed once the event concluded and were succeeded by Regulators.
Informers will disrupt the player's minimap when they player is nearby, which can be used by players to locate the Informer(s). They can also negate Enemy Radar at a radius slightly larger than its minimap disruption radius.
Solo runs typically spawn more Informers than group runs.
Given a large enough radar range, it is possible to detect an Informer with Enemy Radar by staying out of its range with altitude.
Sonar can spot them even when they are disrupting your map.