The brain is a vast, densely interconnected network of neurons computing in parallel. Watching these computations unfold in real time could reveal how the brain processes sensation and guides behavior. But the electrical signals governing the network are fast, faint and notoriously hard to capture in living tissue.

Researchers have developed a breath detector with a chemical sensor that sniffs out when your body is burning fat through a single exhale. Reporting in Device, the handheld, smartphone-assisted device measures acetone—a molecule that is released into the breath when the body burns fat—in about 90 seconds with laboratory-level accuracy.

Implanted medical devices are instruments placed surgically in the body. Many are battery-powered or can be wirelessly recharged. While they can be lifesavers, they are not without problems. They can run out of battery power, and wireless methods for transferring power and data have technical limitations.