On Friday afternoon, about 20 bars around San Francisco are set to have special "facial detection" cameras turned on as part of a new smartphone app by Chicago-based startup SceneTap.

The cameras, which are mounted above the door of their client bars, scan patrons’ faces as they enter and exit the bar. The company’s software then immediately determines whether the person is male or female, and counts how many of each are in the bar, divides that by the known capacity of the bar, and then outputs something like: "Crowd: >90% full | Women: 58% | Men: 42%."

San Francisco bar patrons are unlikely to know that their faces are being scanned, however—the company has only put SceneTap stickers in the windows, but does not explain to customers in an obvious way what exactly is going on.

SceneTap has already been around since last summer in other cities around the country, including Chicago, Austin, Bloomington, Athens, Gainesville, and Madison in around 400 bars. However, the pending launch in San Francisco has caused a bit of a privacy kerfuffle, with the SF Weekly already calling the app "creepy."

"Essentially the goal is to try to create a network that is able to tell you in real-time what a scene is like at a given bar," said Andrew Nieman, the company’s director of business development, in a Thursday night call with Ars.

"As a consumer, let’s say I have some friends in town, I’d like to take them somewhere busy, or conversely I’m going on a date, I want to go somewhere that has some people but is not too busy."

Beyond that, the company hopes bars can use it as a way to analyze promotions (like Ladies’ Night) to see if they’re working. SceneTap says the company plans on making money by selling bar promotions on its website, and eventually adding in-app ads "on a case-by-case basis," and has declined to disclose revenue figures.

The company has painstakingly tried to explain to the public that what it’s doing is facial detection, rather than recognition, as it simply is scanning faces to determine gender and is not comparing that data to other known facial data.

"Here’s the thing—there are no videos or images stored at any time," wrote the company’s CEO, Cole Harper, in an open letter to San Francisco. "Once the data is triggered, the images are overwritten, deleted, gone. There are no tapes. There is no video feed either. No one can go to www.scenetap.com and see what is happening. It’s all data and numbers—that’s it. And since we’re only focused on the door, you’re free to do keg stands and dance like Bernie or hit on that bartender all you want—we do not track you in the venue."

Privacy advocates, researchers remain concerned

Many privacy advocates are concerned that the actual facial data (and not necessarily the image itself) could somehow be linked to an actual person’s identity.

"It is in fact creepy!" wrote Rebecca Jeschke, a digital rights analyst for the EFF, in an e-mail sent to Ars on Thursday. "Looking at the privacy policy, they say they don't keep video or stills, but are silent on if they keep the measurements and other data they collect in order to make their conclusions about gender and age. That's a big question for me."

In an e-mail sent to Ars on Friday, Nieman clarified that the company does not retain facial measurement or related data, despite the fact that this is not reflected in the company's privacy policy.

"The only thing we record is the output of the algorithm: i.e.: male, 27, or female, 23," he wrote.

Despite its use in Facebook (and oddly, art history research), this appears to be the first time that facial recognition technology is being used by a private company in a semi-public space, like a bar. Last year, a similar startup, BarSpace, which put cameras in bars to help customers gauge how busy a bar is via a smartphone app, launched to a similar controversy, but has since folded.

Last year, Alessandro Acquisti, a professor of information technology at Carnegie Mellon University, showed how it was relatively easy to use facial recognition technology to link images to actual people. (The university’s technology, created by a different team of researchers, known as Pittsburgh Pattern Recognition, was acquired by Google.)

"These apps are bridgeheads, or perhaps trojan horses, for more powerful (and probably more intrusive) services to come," wrote Acquisti, in an e-mail sent to Ars on Thursday.

"The fact that, as consumers, we do get eventually habituated to those new services, does not necessarily prove that they come without risks: our attention is captured by what we can see as their immediate benefits—the excitement of using tools that, technologically speaking, are innovative and cool. What we don't see are the long term risks, that more and more information gathered and analyzed about us will allow others to influence and control us. Perhaps that sense of creepiness many feel when they hear about certain identification technologies is nature's way of telling us that something, down the line, may not be right."

San Francisco bars are pulling out

Beyond academics and policy experts, some San Francisco bar owners that originally partnered with SceneTap have said that they’re pulling out and will be taking down the company’s cameras. An increasing number of bars still listed on the SceneTap’s site are now saying that they’re not working with the Chicago startup, including Mr. Smith’s, Southpaw, John Colins, and Bar None.

"We’ve decided that we’re not going live with it," said Charles Hall, the manager of Bar None. Hall originally had told Ars on Thursday afternoon that his bar would be trying out the service, but then called back an hour later to say that he had reconsidered.

"I feel that at this point we have little to gain and a lot to lose until it is made completely transparent as to how [SceneTap is] going to operate the system."