Hotel operators know particular scents can relax guests or, in contrast, make them more alert. Now, Procter & Gamble is bringing the concept of automated scent diffusion to the home At the Consumer Electronics Show in Las Vegas this week, P&G has rolled out a Febreze device that lets consumers release one of two scents into their home by using a smartphone app. All that technology costs $49—or about 17 cans worth of traditional aerosol spray. And yet, some techies have high hopes ...