The current disclosure relates to methods and devices for measuring concentrations of analytes in the gastrointestinal tract of a subject by orally administering a smart pill to the subject, the smart pill comprising two or more sensors, a reference electrode, a power source, a communication interface and electronic circuits, each sensor being able to measure an analyte in the gastrointestinal tract of said subject, wherein the two or more sensors measure different analytes, measuring a concentration of two or more analytes using the two or more sensors, wherein one of the sensors is a pH sensor for measuring hydrogen ions, and wherein the pH sensor is able to locate the smart pill in the gastrointestinal tract by correlating the measured hydrogen ion concentration to a location in the gastrointestinal tract, and transmitting, using the communication interface, the measured concentrations from the two or more sensors to a base device located outside of the body of the subject.