It's hard to find a better example of how technology is revolutionizing patient care than the tiny edible sensor Proteus Biomedical of Redwood City, Calif., plans to begin selling this fall in the United Kingdom.

When the grain-of-sand-sized sensor is integrated into a drug tablet or capsule and activated by stomach fluid, it signals when the medicine was taken to a patch on the patient's body. Then the patch relays the information along with the person's heart rate and other medical…