Proteus’ intelligent pill, named Helius, is designed to be swallowed with medicines. The embedded microprocessor is powered by acid in the stomach in same way as a potato battery. The pill  can then monitor patients’ medication use, compliance with doctors’ instructions or report vital signs. Read more here in a Nature article from 2012.

http://www.nature.com/news/say-hello-to-intelligent-pills-1.9823