After seeing E.T. 17 times, Alvin convinces Theodore to dress up as an alien while Simon builds a UFO to attract more fans. Dave is easily convinced and contacts the news. The call is tapped by some investigators with the government who research UFOs. As Alvin, Simon, and the "alien" depart the crowd of reporters, the investigators decide to kidnap Theodore. The boys pursue on bike to a secret space installation. Once they save Theodore, they hide in a rocket that is launched to Mars.
- The title is a spoof of the words "Unidentfied Flying Object" or "UFO."
- The Chipmunks were inspired after watching Steven Spielberg's 1982 blockbuster, E.T. the Extra-Terrestrial.
- Part of The Alvinnn!!! Edition DVD.