Where do you find the SENTINEL in Arc Raiders?
The SENTINEL spawns on Dam Battlegrounds, The Spaceport, Buried City and The Blue Gate. Spawn points are irregular between raids, so treat the map below as patrol areas rather than fixed positions.

Stationary but deadly turrets that perch on high vantage points. They scan for targets with long-range precision and lock onto players from a distance.
The yellow unarmored canister will be your main target.

Landmarks and extractions on Dam Battlegrounds are shown above. Open the full Dam Battlegrounds map for loot containers and quest markers.
The SENTINEL spawns on Dam Battlegrounds, The Spaceport, Buried City and The Blue Gate. Spawn points are irregular between raids, so treat the map below as patrol areas rather than fixed positions.
The yellow unarmored canister will be your main target. It is rated high threat, so engage it with a plan and an escape route.
The SENTINEL drops ARC Alloy, ARC Coolant, ARC Motion Core, ARC Powercell, ARC Synthetic Resin, ARC Thermo Lining, Heavy Ammo and Sentinel Firing Core.
Destroying the SENTINEL awards 200 XP, and looting its wreck awards 300 XP.
Killing the SENTINEL is worth 500 XP and drops worth roughly 6,482 in total.
The SENTINEL shares its high threat rating with FIREBALL, HORNET and SHREDDER. Compare their weaknesses and drops before choosing what to engage.