In this paper, we propose a new method to detect gastroesophageal reflux wirelessly. Based on passive telemetry using inductive links, impedance of the refluxate can be determined. We have designed and fabricated planar coils integrated with electrodes on flexible substrates using standard photolithography processes. The device can be implanted in the esophagus using currently available clinical techniques. In vitro experiments were conducted by passing different acidic or non-acidic solutions onto the implanted electrodes and measuring the signal amplitudes with an external receiver. Air, drinking water and different concentrations of artificial stomach fluids were used to test the impedance sensor. System configuration, device designs, fabrication processes and measurement results will be presented in this paper.