Omnitrix and Ultimatrix

There are two watches that Ben Tennyson used in the series, the Omnitrix was used in the original Ben 10 and Alien Force while the Ultimatrix was used in Ultimate Alien.

Omnitrix
The Omnitrix is a mysterious watch-like alien device that allows the user to transform into various alien forms by combining the DNA of the selected alien with the user's own DNA, effectively turning them into the alien species the user has selected for 10 minutes. The alien form is selected by 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." In "Secret of the Omnitrix" Azmuth, the Omnitrix's creator tells Ben, that the Omnitrix was originally created to allow the people of the universe a way to "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 minute 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 by 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 by thinking about it, speaking the name its user has given any alien, or turning the badge with the Omnitrix insignia on it. In addition to the aliens that were reprogrammed into the Omnitrix's DNA sequencer by Azmuth, the Omnitrix also possess the ability to absorb DNA samples from other alien species by simply coming into contact with them, effectively downloading a DNA sample and allowing access to that alien form. In the series finale of Alien Force Ben Tennyson gained a new device discribed as the "Ultimate Omnitrix" and thus is appropriately called the Ultimatrix. While lacking a good number of features from the original Omnitrix it does have the "Evolution" feature which allows the user to evolve aliens into new more powerful forms.

Aliens from the Omnitrix
The aliens from this watch who appeared in the original Ben 10 are Heatblast, Wildmutt, Diamondhead, XLR8, Grey Matter, Four Arms, Stinkfly, Ripjaws, Upgrade, Ghostfreak, Cannonbolt, Wildvine, Benwolf, Benmummy, Benvicktor, Upchuck, Ditto, Eye Guy and Way Big. The aliens that were introduced in Alien Force are Swampfire, Echo Echo, Humungousaur, Jetray, Big Chill, Chromastone, Brainstorm, Spidermonkey, Goop, Alien X, Lodestar and Rath.

Ultimatrix
The Ultamatrix was a new watch developed by Azmuth. Azmuth's ex-assistant Albedo stole the Ultamatrix before it could be finished. Eventually, Albedo finished and used it in the last episode of Ben 10 Alien Force. It has the ability to transform the normal aliens in Ben's Omnitrix into their ultimate forms, making them stronger. In the end of the episode, Ben got the Ultimatrix from Albedo by activating the self-destrict for the Ultimatrix and Albedo had to give Ben it so he can turn off the self-destruct. His use of the Ultamatrix became the basis for a new season, Ben 10 Ultimate Alien. The Ultimatrix presented a brand new set of aliens, while retaining all of the Alien Force omnitrix's. So far, seven new Ultimatrix aliens have been chronologically revealed and shown in-use by current-time Ben 10. Some aliens have been revealed to be used in the future and/or have been shown off by a 36-year-old Ben 10,000 in the episode "Ben 10,000 Returns."

Aliens from the Ultimatrix
The ultimate aliens from this watch are Nanomech, Water Hazard, Ampfibian, Armodrillo, Terraspin, NRG, Fasttrack, Clockwork, ChamAlien, Jury Rigg and Eatle.