Scientists have developed a swallowed capsule packed with tiny electronics and millions of genetically engineered living cells that might someday be used to spot health problems from inside the gut.

Researchers at the Massachusetts Institute of Technology tested the device in pigs and it correctly detected signs of bleeding. The results were published Thursday by the journal Science.

With more testing, it could be used in people to find signs of ulcers, inflammatory bowel disease or colon cancer. It's the latest advance in a growing field of sensors that can be worn or swallowed to monitor our health.

Experts say this is the first time engineered cells have been used as sensors in ingestible capsules. The cells detect blood and light up. Electronics then relay signals to a smartphone.