Devices called crystal resonators had the capability to sense gem or crystal concentrations that were abnormally elevated. After the moon of Jedha suffered devastation due to the Galactic Empire's Death Star superweapon in 0 BBY (the year), Imperial troops deployed crystal resonators onto Jedha's terrain to search for kyber crystals. The resonators pinpointed an unusually high concentration within the former location of the Catacombs of Cadera. Upon reviewing these reports, Queen Trios of Shu-Torun (the planet, who was consulting the Empire on kyber crystal extraction and providing resources like miners and tools) questioned Imperial Commander Kanchar, pressing him for information regarding the crystals' presence within the catacombs. Kanchar disclosed that these crystals were those previously pilfered by Saw Gerrera, who headed the insurgent Partisans.
The initial reference to crystal resonators appeared in Star Wars (2015) 39, a comic book penned by Kieron Gillen which was made available on November 22, 2017.