circuits for in vivo telemetric studies of the gastro-intestinal tract. These units could only transmit from a single sensor channel, and were difficult to assemble due to the use of discrete components. The measurement parameters consisted of temperature, pH or pressure, and the first attempts of conducting real-time noninvasive physiological measurements suffered from poor reliability, low sensitivity, and short lifetimes of the devices. The first successful pH gut profiles were achieved in 1972