However, in the reboot series, the Omnitrix can be removed, as seen in the episode "The Most Dangerous Game." In that episode, Ben and Rook go to a planet where aliens are hunted for sport, and Ben has to remove the Omnitrix to avoid being detected by the hunters. He does this by using the Omnitrix's self-destruct mechanism, which forces the device to detach from his wrist. However, this is a risky maneuver that can potentially damage the Omnitrix.
It's important to note that the specific circumstances under which Ben can remove the Omnitrix may vary depending on the different continuities and storylines in the Ben 10 franchise.