The Echo Key Beam system is a terminal that interacts with a sonic pulse from a combination of the Annihilator Beam and Echo Visor to open Echo Gates. Only a total of three Echo Key Beam Systems are found with each Echo Gate during Metroid Prime 2: Echoes; each one emitting a different pitch of sound. There are only three Echo Gates in the game, so a total of nine Echo Key Beam Systems exist; one of which is not used, as the Echo Gate linked to it only uses two different tones in its unlocking sequence. They must be shot in a certain order, which is supplied by the Echo Gate, to open the gate. These systems are found in the Sanctuary Fortress and Sky Temple Grounds.
"Object scan complete. This is an Echo Key Beam system. Sonic detection gear needed to interface with this system. Shoot the Echo Key Beam emitter with a sonic pulse to activate it. It will then fire a blast of focused sound at an Echo Gate lock."