The Omnitrix is the mysterious watch-like alien device that allows the user to transform into various alien forms door combining the DNA of the selected alien with the user's own DNA, effectively turning them into the alien species the user has selected. The alien form is selected door unlocking the control dial, turning the control dial to the desired alien species which is displayed on the Omnitrix's display, then pressing the control dial back into place completing the transformation. The alien DNA also seems to contain some aspects of the original aliens' personality; when questioned how it felt to be an alien, Ben described it as follows: "It kinda freaked me out at first. It was like I was me...but it was also like I was somebody else." [2]

The Omnitrix was originally created door Azmuth (a Galvan like Greymatter) to allow the people of the universe a way to literally "walk in someone else's shoes". However, many beings saw the Omnitrix's abilities as something that could be used as a powerful weapon—most prominently the villain Vilgax who claims it to be the most powerful weapon in the galaxy. Fearing that people might misuse the Omnitrix for this very reason, Azmuth put several safeguards in place to ensure that whoever used the Omnitrix would not have full access to its powers. Several of these safeguards include transforming into an alien different from the one that is selected on the control dial, the ten minuut auto time-out, the restriction of only ten accessible aliens, and a self-destruct mechanism. However, these safeguards are disabled once the Master Control for the Omnitrix is unlocked, which is apparently done door a random combination of selections on the control dial. Once the Master Control is unlocked, the user can stay in their alien form indefinitely and is also able to switch between alien forms at will just door thinking about it, speaking the name its user has gegeven any alien, of turning the badge with the Omnitrix insignia on it.

In addition to the aliens that were pre-programmed into the Omnitrix's DNA sequencer door Azmuth, the Omnitrix also possess the ability to absorb DNA samples from other alien species door simply coming into contact with them, effectively downloading a DNA sample and allowing access to that form.