The jetpack universe is small, but growing. There are similar companies at beaches in New Jersey, Florida and Maryland, where in July the state issued safety regulations for jetpack devices, requiring that customers be at least 16 years old and use a helmet to go more than 10 feet up. In addition to the outposts that Mr. O’Malley operates in Hawaii and San Diego, he plans to open a site at an artificial lake near Las Vegas. But so far Newport Beach appears to be the most popular destination — it is the only beach where a couple has exchanged wedding vows while flying.

The devices once cost roughly $100,000, and the steep price of entry stopped many would-be owners from getting into the business. But now they are a fraction of that; Mr. O’Malley sells a jetpack that attaches to a Jet Ski for $10,000. As other similar devices that rely on water to thrust the wearer into the air have come on the market, businesses started to proliferate. Residents complained about the noise, similar to the Jet Skis that have dominated beaches for years now. Here in Newport Beach, city officials wondered if a rash of injuries would soon come from flying too fast, too high or just too ineptly.

Supporters of the jetpacks say that the devices offer a safer adventure activity than Jet Skiing or paragliding, which have become commonplace in resorts. So far, jetpacks have retained their novelty factor.

“People look up in the sky to see someone flying, and think there’s going to be some sort of alien invasion,” Mr. O’Malley said. “We’ve gotten calls from the police, the Coast Guard, the F.A.A. — people just don’t know how to respond.”

Operating the devices is somewhat similar to controlling a video game joystick: Riders are strapped to a large seatlike contraption and outfitted with a helmet that allows them to hear an instructor giving guidance through a walkie-talkie. For rookie pilots, the instructor holds a remote that allows control of how much water force is used.