For you vets, there is no need to explain the brilliance of Castle's gimmicks, but noobs...read on. All of gimmicks listed are from Wikipedia.
1.) "Insured by Death by Fright"
Macabre (1958): A certificate for a $1,000 life insurance policy from Lloyd's of London was given to each customer in case he/she should die of fright during the film
House on Haunted Hill (1959): Filmed in "Emergo". An inflatable glow in the dark skeleton attached to a wire floated over the audience during the final moments of some showings of the film to parallel the action on the screen when a skeleton arose from a vat of acid and pursued the villainous wife of Vincent Price. The gimmick did not always instill fright; sometimes the skeleton became a target for some audience members who hurled candy boxes, soda cups or any other objects at hand at the skeleton
The Tingler (1959): Filmed in "Percepto". In the film a docile creature that lives in the spinal cord is activated by fright, and can only be destroyed by screaming. In the film's finale one of the creatures removed from the spine of a mute woman killed by it when she was unable to scream is let loose in a movie theatre. Some seats in theatres showing the Tingler were equipped with larger versions of the hand-held joy buzzers attached to the underside of the seats. When the Tingler in the film attacked the audience the buzzers were activated as a voice encouraged the real audience to "Scream - scream for your lives."
13 Ghosts (1960): Filmed in "Illusion-O". A hand held ghost viewer/remover with strips of red and blue cellophane was given out to use during certain segments of the film. By looking through either the red or blue cellophane the audience was able to either see or remove the ghosts if they were too frightening
5.) "Fright Break"
Homicidal (1961): This film contained a "Fright break" with a 45 second timer overlaid over the film's climax as the heroine approached a house harboring a sadistic killer. A voiceover advised the audience of the time remaining in which they could leave the theatre and receive a full refund if they were too frightened to see the remainder of the film. To ensure the more wily patrons did not simply stay for a second showing and leave during the finale Castle had different color tickets printed for each show. In a trailer for the film, Castle explained the use of the Coward's Certificate and admonished the viewer to not reveal the ending of the film to friends, "or they will kill you. If they don't, I will."
6.) "The Punishment Poll"
Mr. Sardonicus (1961): In this gothic tale set in 1880 London a baron's face is frozen into a permanent grotesque hideous smile after digging up his father's grave to retrieve a lottery ticket left in the pocket of his father's jacket. The audiences were allowed to vote in a "punishment poll" during the climax of the film - Castle himself appears on screen to explain to the audience their options. Each member of the audience was given a card with a glow in the dark thumb they could hold either up or down to decide if Mr. Sardonicus would be cured or die during the end of the film. Supposedly, no audience ever offered mercy so the alternate ending was never screened.
Castle had other gimmicks but these seemed to be the best of the bunch. Castle's filmography is filled with a variety of films ranging from horror to drama. But he is ever known as the PT Barnum of movies.
3-D may be the gimmick of today but the past was indeed the golden age of gimmicky cinema.
Which William Castle gimmick is your favorite?