Systems and methods for mobile real-time breath ketone and exhaled gas detectors are described. For example, a device comprises an opening, providing a flow path through which a person breathes, a sensor, providing a ketone signal corresponding to a concentration of a respiratory component in exhalations of the person and including metabolic data, wherein the concentration of the respiratory component is associated with a level of ketone bodies in blood of the person, a display, and an electronic circuit, receiving the ketone signal and the metabolic data and providing a visual indication of the ketone signal and the metabolic data on the display.
