The House of El Device or Kryptonian Command Key was a tool created by Jor-El that was sent to the planet Earth along with his son Kal-El. It can be used to access Kal-El's Spaceship and the Fortress of Solitude.
This device would be influential in helping Clark Kent realize who he was and what he could do to protect the planet as the hero, Superman.
Jor-El formed the Command Key on Krypton just before placing his son Kal-El in a ship that would be sent to Earth where he would escape Krypton's destruction. He put the Key in the ship with Kal-El and launched him to Earth.
The ship landed in Smallville, Kansas in a field of the Kent Farm. The ship was found by Jonathan and Martha Kent who took in Kal-El as their own and hid the ship beneath their barn. When Kal-El, now named Clark Kent, was 13, Jonathan showed him his ship and the Command Key, which Clark wore around his neck from that point on.
Twenty years later, when Clark grew into adulthood, he heeded his late father's words and went on a journey to find out more about his origins, with the Command Key still around his neck. Whilst overhearing two soldiers speaking about an alien ship on Ellesmere Island, Clark traveled there and burred through the ice with his Heat Vision, passing the ship's defenses and plugged his Command Key into a fitting socket, finally bringing Clark him face to face with a projection of his biological father - Jor-El. Jor-El informed his son of his alien heritage and purpose on Earth, before moving the ship to a nearby mountain top. Embracing himself as Kal-El, Clark donned a red-and-blue caped Kryptonian skinsuit and began testing the limits of his superpowers, finally learning how to fly.
Shortly thereafter, General Zod showed up on Earth after Kal-El and the Growth Codex, which was sent with the latter. When Kal-El surrended to be handed over to Zod, he gave Lois Lane his Command Key (behind Faora's back). When Lois was thrown in a holding cell aboard the Black Zero, she plugged the Key into a socket, which activated Jor-El's projection, which told her how to defeat the invading Kryptonians (a plan she later relayed to Clark) and promptly guided her to the safety of an escape pod, before changing the atmosphere to that of Earth allowing Kal-El to regain his powers and escape.
The plan as to put Kal's ship aboard a military transport aircraft to use as a makeshift bomb against the Black Zero, since a collision between 2 Phantom Drives would generate a Phantom energy singularity, that would re-imprison Zod and his forces in the Zone. Lois tried to insert the Command Key into the ship, but it wouldn't accept it. Unable to put it in, Lois was blown out, as Faora-Ul came to stop the plane and undermine the plan. Fortunately, Emil Hamilton managed to work out that the pod needed turning, and inserted the key, activating the Phantom Drive, and sending all things near (including the Command Key) into the Phantom Zone.
Prisoners sentenced to the Phantom Zone were placed under a "somatic fugue", a state of semi-unconsciousness, whilst they were reprogrammed using subliminal teaching methods. The ultimate aim was to eventually return them to normal Kryptonian society as rehabilitated individuals.
In theory, every exile was to be released — eventually — after cycles of solitude and subliminal conditioning had curbed their antisocial tendencies.