Revealed

Hunters can utilize several game mechanics to reveal Scavengers. A revealed Scavenger will have a red outline around them, which is visible across the map and through terrain.

Drones
If a Drone is activated, it will float into the air and project a red cone beneath it. Any Scavenger that enters this cone, will hear a load alert and see their own red outline. They will be revealed to other Scavengers and the Hunter, until they either leave the area, the Drone is disabled, the Scavenger stands in the center of a Smoke Screen or are put in stealth by the Active Camo ability. Downed Scavengers cannot be revealed by Drones.

Blood Mode
When Blood Mode activates, the 2 exits will fire a pulse which will spread around the map in 2 circles. The Scavenger can see the pulse coming and will be revealed the moment it hits them. Active Camo and Smoke Screen can be used to temporarily remove the Revealed effect.

Hunter Perks
Hey, Down There is a Stalker Perk which will reveal a Scavenger for a few seconds after they have been downed.

Trivia

 * Although this technically does not apply the revealed effect, observant Hunters can track Scavengers even when they are hiding or stealthed by looking for several clues, like the black silhouette when Scavengers are stealthed, the bar with the current health visible above the Scavengers' head when they have recently taken damage, the dust being kicked up by stealthed running Scavengers, bushes moving and Scavenger sounds.
 * If the Scavenger that summoned the Clone has the revealed effect, the Clone itself will also have the revealed effect, provided the Clone meets the conditions to be revealed (ie. Also in the Drone's cone.