An Echo Gate is a device in Metroid Prime 2: Echoes that uses a sonic security system. In order to open these, the Echo Visor must be acquired, as well as the Annihilator Beam. The locks are easily recognized by a "key" symbol while using the Echo Visor, and are in the shape of small terminals. Unlocking the Echo Gates can sometimes be a bit tricky. To do so, Samus must first shoot the Echo Gate itself, doing so will release several "echoes" of different pitch. To open the gate, Samus must find and shoot the Echo Key Beams in the order in which the "echoes" sounded. Each Echo Key Beam has its own "echo" corresponding to the ones made by the Echo Gate. However, if one lock is unlocked out of order, Samus must restart the unlocking sequence.
"Object scan complete. This door uses a sonic security system. Sonic detection gear needed to interface with this system. Shoot the Echo Gate with a sonic pulse to learn the combination of its sonic locks. Unlock the locks in this sequence to advance."