The dialog was recorded first and then the actors had to rehearse and lip-sync to the prerecorded dialog during the takes. This is the opposite of the normal procedure in which an actor's dialog may be looped during post production.
The filmmaker was on such a tight budget that the film's ultimate weapon, the "focusing disintegrator", was actually a Hubley's Atomic Disintegrator toy cap gun, bought for a dime, with a flashbulb added as a beam. (In some scenes the words "Hubley's" can clearly be seen embossed on the side of the gun.) Atomic Disintegrators can be bought today on eBay for upwards of $300.
Unable to afford time on a soundstage to film Betty Morgan's home, director Tom Graeff posed as a UCLA student directing a student project, and so obtained permission from an elderly woman to film for free in her home.
One skeleton was used for every dead body in the film. A hook/tag on the head and identification markings in permanent marker on the hip can clearly be seen on the skeleton in almost every scene. The skeleton also has curiously bolted limbs.
Although Warner Bros. distributed this ultra-low-budget sci-fi film, it was definitely not a Warner Bros. production. The studio needed a genre film to play as the second feature with the Godzilla sequel it was releasing under the title "Gigantis, The Fire Monster" (1959) and bought this from producer Tom Graeff.
Dawn Anderson, who played Betty, was actually a former child actress named Dawn Bender (Anderson was her married name). Like most movie teenagers of the period, she was in her early 20s when this film was shot.
Director, writer, and co-star Tom Graeff made Teenagers from Outer Space as a vehicle for his boyfriend Charles Robert Kaltenthaler, who starred in the film as Derek. Kaltenthaler was credited as David Love in the film. It would be the young actor's second and final film.
For many years, actor David Love was thought to be writer/producer/director Tom Graeff. Graeff does appear in the film, playing Joe under the name Tom Lockyear. David Love was actually named Charles Robert Kaltenthaler.
The trivia item below may give away important plot points.
In the film's finale when the invading spaceships are suppose to be crashing to earth, the budget couldn't produce a believable special effect for this so stock footage of an erupting volcano was used.