Zirx agent Ian Henderson, 26, of Germantown, Md., awaits his next fare in Franklin Square. (Faiz Siddiqui/The Washington Post)

Tony Malba had circled Penn Quarter one too many times on a recent Saturday evening. So instead of prolonging the futile search for parking, he tapped an app on his phone and put his Mitsubishi in the hands of a stranger while he dined at Hill Country Barbecue Market with his wife.

When they were ready to leave, he tapped the app again. An agent showed up and turned over the SUV — and they drove home to Alexandria.

By now, most people are familiar with ride-hailing services such as Uber and Lyft, which have become as ubiquitous as taxicabs in major cities. Lesser known are the on-demand valet and concierge services, which promise to solve your parking problem while in the process offering to fill up your gas tank, wash your car, change the oil or charge the battery.

With the touch of a button, you summon not a vehicle but rather a yellow-clad agent to commandeer yours. Once the valet arrives, usually on a scooter or skateboard or bicycle, you exchange a code and hand over the keys. Then, freed from the worry of finding a parking space, you proceed to your workplace, restaurant or nightspot before, hours later, you launch the app, touch an icon and — voila — your car reappears.

Some are calling it the “reverse Uber.”

“It’s become an everyday habit,” said Malba, 49, who said he spends about $9 a day on the Zirx valet service. “It’s super convenient.”

There’s one caveat: You might not know where your car’s been all that time.

“The first time you use Zirx, it’s a little bit of a strange experience,” chief executive Sean Behr said. “The fact that you’re having dessert at a restaurant and you press a button and you watch as a car drives to you. It is off-putting the first time you do it.”

Zirx parks cars in various garages in downtown D.C., but it doesn’t specify their locations — apparently for security reasons. A tour of the garages on a recent weekday revealed dozens of spaces leased and filled with a mix of sports cars, SUVs and sedans. Keys are stored in passcode-activated safes.

It’s another product of the sharing economy, where independent contractors take on the burden of everyday tasks for customers willing to pay.

Already, “parking wars” have heated up among valet apps in densely populated cities such as San Francisco, where a mix of pastel blazers has colored city streets: blue for Luxe, yellow for Zirx and pink for Carbon.

Lest you find it unsettling to leave your car in the possession of a stranger, as Malba initially did, the companies say they have you covered: Zirx has a $1 million insurance policy on the car and another million on the agent driving the vehicle. Luxe is covered for $5 million in general liability and also has a $1 million insurance policy for garage keepers.

“It was a little weird in the beginning. It’s a little disconcerting,” said Malba, who uses Zirx to park his SUV outside his office at 18th and K streets NW most mornings.

Like Uber and Lyft when they launched, questions have been raised about the legality and licensing requirements of the relatively new services. While Zirx offers discounted prices in certain “DropSpots,” its operations are not confined to any particular location — so a public-space permit isn’t required, the District Department of Transportation said.

Companies that provide valet parking at a specific location, such as a special event or restaurant, are required to have a permit to operate. “DDOT does not require a public-space permit for businesses providing individual valet parking,” DDOT spokesman Terry Owens said. “If the business model were to change, DDOT would reconsider.”

Zirx says it is registered with the Department of Consumer and Regulatory Affairs to operate on-demand car and concierge services and that it has been awarded a business license by the District.

Luxe, which says it has raised about $25 million in capital but doesn’t yet operate in the District, says its 1,000-plus valets have racked up more than 30,000 miles of traveling in eight cities. More than 80 percent of its users become repeat customers, it says, an indicator that business analysts use to determine whether new products are sustainable.

Still, analysts say it’s too early to tell whether the apps will gain traction or are just the latest fad. Julie A. Ask, a mobile analyst for the technology and market-research company Forrester, said the apps attract loyal audiences because they give customers an array of options.

Loyalty, however, doesn’t mean growth. Right now, Zirx charges $10 for all-day parking or $199 monthly for customers who sign up by Dec. 31 — compared with $10 to $20 per day for typical daily garage parking downtown.

“Consumers in this situation are not that price sensitive,” Ask said. Erasing the inconvenience of having to find a garage parking spot, she said, is what could make valet apps attractive — not just shaving a few dollars off the price tag.

“More consumers would be willing to drive and park in a garage if they knew where, when, how much, etc.,” she said.

Michael Miele, a Tufts University graduate who initially was looking to develop an app similar to Luxe and Zirx, decided against it after evaluating the business potential. Instead, he developed a software framework — SpotLight Parking — that garages and valet operators can use to run existing businesses.

“Realistically, it’s almost impossible to make it profitable,” he said of on-demand valet services.

“It can be profitable if you assume a steady flow of parking demand over the course of the day. . . . If you have them standing around all day doing nothing, you’re just burning money.”

But investors see potential. So far, they’ve put more than $36 million into Zirx, which has secured funding from Bessemer Venture Partners, BMW iVentures and others. And it employs about 400 drivers nationwide, paid contractors who make an hourly wage and earn bonuses depending on customer volume, company officials said.

Agents must be licensed drivers 21 or older who can pass a seven-year background check and also have a clean DMV record.

Ian Henderson, 26, of Germantown, Md., whirls around downtown Washington on his big-wheeled Razor scooter, making an estimated 15 to 20 car trips a day. The onetime Uber driver said he joined Zirx in June after deciding that Uber had taken too much of a toll on his car.

“Obviously, it’s less than you’d make on a certain job for Uber, but you have a lot less expenses as well,” he said. Henderson added that demand slows nearly to a halt by the afternoon, when cars have been parked, but picks up again by the evening, when those customers need their cars back.

“It’s kind of like a pop-up garage, if you will,” said Ethan Kurzweil, a partner with Bessemer who was involved in the firm’s $14 million investment in Zirx. “I don’t think there’s an at-scale valet service that exists at all. For Zirx, it will be less and less of the primary offering over time as well. I think it’ll be a mix of services, one of which is valet, over time.”

And while San Francisco-based Zirx and Luxe offer a similar catalogue of services, there are key differences.

Luxe, for example, offers a designated driver service for customers too impaired to drive their cars home. It requires no passcode and specifies where cars are parked.

“If you had a little bit too much to drink, our valet will pick you up,” chief executive Curtis Lee said. The cost, the company says, starts at $15 for up to 5 miles, $30 up to 15 miles, $60 up to 30 miles and $100 for up to 50 miles.

Luxe, which operates in eight cities, is eyeing an expansion into the District, which is notorious for bad parking and whose parking shortage has prompted a smart-parking pilot program in one of its most crowded corridors.

“The analogy is that you store your car in the cloud with us,” Lee said. “And you can pull your car whenever you want. It’s kind of like having a remote control.”

Kurzweil, the partner with Bessemer, acknowledged that many questions remain on the subject of valet apps — whether they’ll catch on, face regulatory hurdles or become a premium service for the wealthy.

“The overriding answer to all of them is, ‘We’ll see,’ ” he said.