Seeker Missile

The Seeker Missile upgrade (previously known as the Seeker Launcher) allows Samus Aran to simultaneously fire up to five normal Missiles at up to five targets. Seeker Missiles can also be used to fire more than one Missile at each target. Using the Seeker Missile is a must to pass some of the puzzles in Metroid Prime 2: Echoes. Though it is rarely necessary for combat, it is obtained at the Hall of Honored Dead in the Temple Grounds below the Great Temple after defeating the Boost Guardian.

Samus is also able to obtain the Seeker Missile in Metroid Prime 3: Corruption. This time, it appears to be of Space Pirate origin. However, it is obtained in Xenoresearch B, Eastern SkyTown. This suggests that the Pirates may have stolen the technology while they were on Aether. It could also be the result of a trade between the Chozo and the Luminoth, which the Pirates came across and examined. It may also be a different version developed by the Chozo. The Seeker Missile can harm Helios in his disk form and are used to open Multi-Lock Blast Shields and locks on SkyTown and other areas by destroying several locks simultaneously. Notably, it is somewhat harder for all the Missiles to hit the desired targets in the game, as Corruption uses a different Missile type than in the previous two Prime games. Samus can also fire up to five missiles in Metroid Prime Pinball, though they do not lock on and move faster, like the normal Missiles in that game or the 2-D games.

In Metroid: Other M, Samus obtains the Seekers again and uses them much like she did in the Prime series games, while being the first non-Prime game to feature the item. However, unlike the Prime Seekers, one of the five Missiles is actually a Super Missile. They are obtained by defeating the Rhedogian (which was actually using the upgrade against Samus) in the fourth encounter. In order to fire the Seekers, a Super Missile must be charged. Afterwards, it may lock onto up to five different targets as long as four other targets are within view. Like in the Prime series, the weapon can open Multi-Lock Blast Shields.

Metroid: Other M manual
"If you press and hold A until the Charge Gauge is fully charged, you'll lock on multiple targets. Release A to fire a Super Missile along with four normal missiles toward up to four additional targets."

Metroid: Other M Status screen data
"Effect: Launches multiple missiles simultaneously. Controls: Charge up a Super Missile . When multiple targets are locked, fire."

Trivia

 * In the Prime series, the player has to fire a missile and hold the missile button in order to charge the Seeker Missiles. However, if the player uses the Charge Beam, release the shot, then holds down the missile button immediately afterward, the Seeker Missile targeting reticule appears, thereby saving the player a missile.
 * In Corruption, Samus can execute three extra procedures to prevent her having to waste a Missile before charging the Seeker Missile. She can either shoot once then immediately hit the missile button (which requires good timing), use the Screw Attack and hold the Missile button, or turn on the Scan Visor then exit and charge missiles before the Arm Cannon comes up. Note that the Visor method has an effect on the Arm Cannon. Instead of the Arm Cannon closing then opening at the front section, it retains its shape and the front part doesn't open out, but the glow appears. Once it is fired, it does go to the missile firing animation.
 * Meta Ridley, the Metroid Prime, and the Rhedogian have a "Multi-Missile System" attack which fires simultaneous homing projectiles at Samus.
 * In Other M, the Seekers are actually not an authorized item, but rather, a power-up dropped by the Rhedogian. This, along with the Diffusion Beam, makes it one of the only two upgrades that were not obtained in Super Metroid.
 * In Other M, no matter how many enemies Samus targets with the Seeker Missiles, five missiles will always be used.
 * In Other M, the Seekers play a lesser role; there are only three Multi-Lock Blast Shields within the game and the Seekers are not used in boss fights.
 * Bryan Walker stated in the Trilogy developer interview that his favorite weapon was the Seeker Missile.
 * The ability to lock on up to 5 targets at once is very similar to the targeting method of some types of boomerangs in the Legend of Zelda series.