SAN FRANCISCO -

A watchful eye is coming to San Francisco's bar scene, but not to keep you in check. It just wants to check you out.
  

A new app launched this weekend that will scan the faces of patrons in 25 bars across the city to determine their ages and genders.
  

Would-be customers can then check their smartphones for real-time updates on the crowd size, average age and men-to-women mix to decide whether the scene is to their liking.
  

The Austin, Texas-based makers of SceneTap say the app doesn't identify specific individuals or save personal information.
  

But in a city known for its love of both libations and civil liberties, a backlash erupted even before the first cameras were switched on from bar-goers who said they would boycott any venue with SceneTap.