The Omnitrix was a device that featured Ben 10.
In order to stop a war with the Highbreed, Ben Tennyson used the Omnitrix to reverse the genetic damage of the entire species by infusing them with random DNA from various alien races thus saving them from genetic extinction. Saved from death, the Highbreed called off their invasion forces though this act consumed most of the power of the Omnitrix leading it to be reset and forcing Ben Tennyson to unlock a new set of aliens present within the device. (EP: War of the Worlds)
The Omitrix contained a special master override control allowing for the full power of the device to be accessed by the user. Through a voice command by its creator, this master control could be unlocked for the benefit of the machines wearer. There were a recorded number of one million nine hundred and three genetic samples within the Omitrix allowing a potential user to access any such alien within the recorded database. However, typically these alien samples were in sets of ten which was done so for simplicity sake. When master control was given, a simple voice command allowed the user to transform into any alien present within the Omitrix. (EP: War of the Worlds)
Another noted ability of the Omitrix was the capacity to repair genetic damage. By analysing an individual's body, the device was capable of noting the damage sustained and assessing whether it could be repair. This allowed it to remove a simple infestation such as a Xenocytes on a Human or reverse the genetic damage to an entire species. The latter act, however, consumed the entire energy store of the device and resetted it thus removing the master control and shifting to another random set of alien forms which the user had to unlock once more. (EP: War of the Worlds)
The creator of the Omnitrix had a another reason for the creation of the device. The fact that it contained DNA samples from millions of species meant that it could serve a potential tool in regards to those races that were exterminated by war. Using the DNA sample, the Omnitrix was said to help resurrect such races making it an important artifact. (EP: War of the Worlds)