Sentinel Crystals are a form of Xenotech device found in the upper section of the Torvus Bog in Metroid Prime 2: Echoes. They were developed by the Luminoth during the war against the Ing, and were used to monitor key areas for Ing Horde activity. They are apparently extremely durable, as only the strongest Ing could damage them, but were somewhat less effective in the Ing's home dimension of Dark Aether. When Samus Aran arrives on Aether, some Sentinel Crystals are still active, the last remaining ones being used by U-Mos to monitor the planet for Ing movements. This is likely how U-Mos is able to inform Samus that the Ing are increasing their forces in the Torvus Bog after she steals the Light of Aether back from the Dark Agon Wastes.

On their away missions to Dark Aether, the Luminoth were able to deploy Sentinel Crystals there as well. However, they soon discovered that the Sentinel Crystals in place there proved unable to remain active for long periods of time, due to constant exposure to the dark planet's poisonous atmosphere and its inhabitants' attacks. As a result, the Luminoth turned to the creation of the Dark Sentinel Crystals to function in a dark environment.

Sentinel Crystals and their dark counterparts are similar to Airthorns, in which they were all built by Luminoth in order to inform them on any activity and possible danger from enemy forces on both light and dark planets, except that the latter mechanoid is designed to monitor local airspace.

Official data

Logbook entry