‘Spy Kids’ adds smell with ‘4-D’ Aroma-Scope

Rodriguez calls his gimmick “Aroma-Scope.’’ He tried it out at test screenings and found that children and parents had a good time with it.

“When it came time to do `Spy Kids 4,’ I couldn’t just go back and do 3-D like everybody else is now. I had to bring something extra,’’ Rodriguez said. “Just watching my own kids with interactive gaming, you ask them to watch a movie, it just feels so passive to them. I thought, this helps bridge the gap. It’s an interactive thing, almost like playing a game while you’re watching the movie.’’

The idea dates back to John Waters’ 1981 suburban satire “Polyester,’’ released in “Odorama,’’ with viewers given similar scratch-and-sniff cards. The 2003 animated tale “Rugrats Go Wild’’ also used cards to add scent to the picture.

The new “Spy Kids,’’ opening Friday and playing in both 2-D and 3-D versions, uses its odors (offered in both formats) to complement the story as a retired operative (Jessica Alba) is called back to service to fight a villain who has speeded up time, threatening to bring about a quick end to the world.

She’s kept her vocation a secret from her new husband (Joel McHale), but her step-kids (Rowan Blanchard and Mason Cook) wind up pressed into the action, aided by the now grown-up original spy kids (Alexa Vega and Daryl Sabara) from the first three movies.

The smells from the scratch-and-sniff cards are mostly pleasant. However, with a bit of raunchy humor, including gags about a spy baby’s diapers, viewers should expect at least one off odor.

“Originally, we didn’t have any really rancid smells, but kids wanted something really stinky in there,’’ Rodriguez said. “It really doesn’t smell that bad. No one’s going to get sick in the theater.’’

Rodriguez’s Aroma-Scope follows a long tradition of adding something extra to the movies.

Filmmakers began trying gimmicks to hang onto audiences as television eroded movie attendance in the late 1940s and early 1950s. Most were short-lived or one-time tricks, such as early tries at 3-D cinema or such odor-adding processes as Smell-O-Vision, in which scents were piped into theaters.