Patrons of about two dozen San Francisco bars will soon find a new set of notices and cameras inside, but they won't be for security purposes. Instead, it's the work of SceneTap, a social app that detects the age, gender, and number of people in order to let both patrons and owners know what kind of crowd the bar has at any given moment. Starting May 18th, customers in San Francisco will be able to use the Android, iOS, or web app to find bars that are "chill" or "hoppin," those that skew male or female, or those with younger or older patrons. Owners, meanwhile, can get a more accurate headcount and see whether deals designed to attract certain demographics are working out. And everybody will be caught and analyzed on video.

SceneTap, which launched last year and currently serves six cities, uses cameras installed in bars to gather pictures of patrons and analyze their facial characteristics. It stresses that it doesn't make these images public, nor does it try to identify the people it's looking at. "It's an algorithm behind the scenes that's trying to figure out what you look like," says CEO Cole Harper. "Do you look like a male or female? A 22-year-old or a 25-year-old?" According to Harper, it's about 85 percent accurate in determining gender, 90 percent accurate on determining age within six years, and 80 percent accurate within three years. It can also count people entering and leaving with between 85 and 98 percent accuracy, he says.

Unsurprisingly, the app's launch has been controversial. The SceneTap Twitter feed has spent the last day fielding questions from users who worry that they're being spied on or used as bait for prospective customers. Customers are notified at the bar's entrance that they're being recorded, a spokesperson says, and it's vetted its system with the FTC. Images are sent to off-site servers, data is not recorded or stored, and bar owners don't have access to the feed, just the demographics.

Nonetheless, we imagine some people will be made uncomfortable both by the fact that they are being — however discreetly — watched and by the explicit use of patrons' age and gender to draw potential customers. There are other reasons, like check-in specials, to use the app, but gender metrics make up an overwhelming amount of the news feed: "The ladies love [x]!" followed by a percentage is by far the most common message. SceneTap is using some interesting analytical tools, though, and if it works as well as it claims to, we're a bit surprised it isn't already showing up elsewhere.