According to the director, R.W. Goodwin, he feels that Alien Trespass has its roots in genre classics The War of the Worlds (1953), It Came from Outer Space (1953) and The Day the Earth Stood Still (1951), as well as The Blob, and It Conquered the World.
The movie theater where the alien creature attacks movie goers is showing The Blob (1958). That movie contains a scene in which an alien creature attacks movie goers in a theater.
Alien Trespass's saturated color was inspired by the original The War of the Worlds (1953) - one of Goodwin's favorite sci-fi films.
Pay careful attention to the alien monster that's eating everyone. It's giant eye is reminiscent of the monster from The Crawling Eye (The Trollenberg Terror) and it's tentacle, with its sucker grips is very reminiscent of the silicate monster from Island of Terror.