First appearance: Earth vs. the Flying Saucers (1956)
A scientist working on a secret rocket project gets contacted by aliens who tell him to "cut it out."
He doesn't listen so the aliens blow up the rocket base. Understandably this angers the scientist so he develops a sonic weapon to fight the aliens. Based on a true pamphlet.
On a side note. I love how the saucers in this movie are stop motion creations from Ray Harryhausen.