Surveillance tools to detect drowning swimmers

From Technology Review‘s “Big Brother Logs On“:

Consider the benefits of the “computer-aided drowning detection and prevention” system that Boulogne, France-based Poseidon Technologies has installed in nine swimming pools in France, England, the Netherlands and Canada. In these systems, a collection of overhead and in-pool cameras relentlessly monitors pool activity. The video signals feed into a central processor running a machine perception algorithm that can effectively spot when active nonwater objects, such as swimmers, become still for more than a few seconds. When that happens, a red alarm light flashes at a poolside laptop workstation and lifeguards are alerted via waterproof pagers. Last November, a Poseidon system at the Jean Blanchet Aquatic Center in Ancenis, Loire-Atlantique, France, alerted lifeguards in time to rescue a swimmer on the verge of drowning. Pulled from the water unconscious, the swimmer walked away from a hospital the next day.