Invasion of the Saucer-Men
(1957)

The Saucermen are vulnerable to light, so a group of teenagers surround them with their cars, causing the Saucermen to go up in smoke, but one of the Saucermen's severed hands (complete with eyeball) is still at large. (The sequel, alas, never came)

Thanks Evil Ed! ( I think)

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Read more about this film at The Internet Movie Database.