Phones or watches may be smart enough to detect sound, light, motion, touch, direction, acceleration and even the weather, but they can't smell. This has created a technology bottleneck that companies have spent more than a decade trying to fill. Most have failed.A powerful portable electronic nose, said Redg Snodgrass, a venture capitalist funding hardware start-ups, would open up new horizons for health, food, personal hygiene and even security.Imagine, he said, being able to analyse what someone has eaten or drunk based on the chemicals they emit; detect disease early via an app; or smell the fear in a terrorist.Aborted projects and failed companies litter the aroma-sensing landscape. But that's not stopping newcomers from trying.Like Tristan Rousselle's Grenoble-based Aryballe Technologies, which recently showed off a prototype of NeOse, a hand-held device he said would initially detect up to 50 common odours.The problem, said David Edwards, a chemical engineer at Harvard University, is that, unlike light and sound, scent is not energy, but mass: "It's a different kind of signal."That means each smell requires a different kind of sensor, making devices bulky and limited in what they can do. The aroma of coffee, for example, consists of more than 600 components.France's Alpha MOS was first to build electronic noses for limited industrial use but its foray into developing a smaller model that would do more has run aground.Adamant Technologies, which in 2013 promised a device that would wirelessly connect to smartphones and measure a user's health from his breath, has also gone quiet.Partly the problem is that we still don't understand well how humans and animals detect and interpret smells, said Chris Hanson, CEO of EssenceChip.Snodgrass is funding a start-up called Tzoa, a wearable that measures air quality. He said interest in this from polluted China was strong. Another, Nima, raised $9-million last month to build devices that can test food for proteins and substances, including gluten, peanuts and milk. Its first product will be available shortly, it said. ..