Good luck getting away with fibbing to the doc who prescribes you this nifty contraption. The FDA has approved a digital sensor that can be swallowed in a pill to monitor your health from the inside. Doctors can also keep track of whether patients are taking their medications regularly and properly, and determine if medications are effective. Roughly the size of a grain of sand, the “digital pill” is powered by water, or stomach fluid, which then “communicates a unique signal that determines identity and timing of ingestion,” its manufacturer said Thursday. It passes easily through the body and is excreted like high-fiber food.