The Grustrag Three Beacon is one-time use a gear item used to lure the Grustrag Three out of hiding.
Acquisition
The Grustrag Three Beacon can be purchased off Baro Ki'Teer in the Concourse section of the TennoRelay for 125,000 Credits 125,000 and 200 200. Note that Baro Ki'Teer's stock changes with each appearance and this item may not be available on a succeeding appearance.
Notes
To use the beacon you must equip it on your gear wheel which can be done in the equippment menu.
The beacon can only be used in a mission where assassins are able to spawn. Visit Death Mark for more information on eligible locations.