If you live in a polluted city, which means any major city in the world and thousands of smaller ones, too, air pollution is both a problem and a danger. The Flow tracker keeps you informed as to what’s what in the atmosphere around you, tracking particulate matter (PM2.5), nitrogen dioxide, ozone, volatile organic compounds (VOCs), temperature and humidity, so you can decide whether to venture outdoors or stay safely inside. It’s a small device you can clip to a bag or your clothes. Additionally, there’s an app that covers more than 150 cities worldwide, with more coming online every day, so it can provide info that not only tells you what’s in the air at all times but also forecast what’s coming. As one tech site notes, it’s a Fitbit for air quality, and, at least to us, tracking the quality of the air you’re breathing is more important than adding up the steps you take, especially if those steps are trudged through dirty, disgusting air.