Topher White founded the nonprofit Rainforest Connection with the intent of creating a low-cost monitor that could help remote communities in their efforts to halt illegal logging, which is an enormous threat to tropical habitats. As it turns out, the best way to track people who are cutting down trees is sound. Using old cell phones linked to an artificial-intelligence platform in the cloud, White developed a system that can detect chainsaws in real time and send automated alerts to authorities. Today, Rainforest Connection is recording audio continuously from over a 1,000-square-miles of forest across 12 countries. That scale, along with rapid improvements in machine learning, have opened up tantalizing possibilities for understanding what the sounds of nature really mean.