In the latest twist on an edible sensor that could one day monitor disease, scientists have created a pill-size device that can detect bleeding deep inside a pig’s digestive tract—and relay that information via a wireless signal to a cellphone. If researchers can modify the sensor to pick up other chemicals—and shrink the pill—they could one day create a multipurpose readout of gut health.

To make their sensor, engineers and biologists turned to a bacterium commonly sold as a probiotic in Europe. They genetically engineered it to detect the blood chemical heme by injecting several genes: one that triggers in the presence of heme, and another that makes the cell glow when triggered—enough to light up a detector and produce a wireless signal.

They packaged the 44 million bacteria—along with a battery, light detector, and other electronics—into 10-millimeter-by-30-millimeter pills, which they fed to three pigs. Only pigs with blood in their guts triggered the sensor , the researchers report today in Science .

Other devices have already been created to detect gases in the gut and remotely control sensors using magnets . By picking up on the body’s chemicals and containing several versions of the bacterium, a “super” sensor could one day provide information about cancer, ulcers, or other conditions, the researchers note. Such a supersensor could be a long time coming, other researchers say. For now, the team is trying to shrink this pill by two-thirds by reducing the power demands and the battery size.