Note that we are talking pigs here.
According to the abstract the researchers “combined biosensor bacteria with a miniaturised wireless readout capsule to produce a minimally invasive device capable of in vivo biosensing in harsh, difficult‑to‑access environments”.
Specifically, it was used to measure gastrointestinal bleeding in pigs.
Researchers believe the resilient biosensor can also be altered to enable its use in detecting other ailments.
The capsule, a micro-bio-electronic device (Imbed) contains miniaturised luminescence readout electronics that wirelessly communicate with an external device, delivering real-time information from within the body.
Image source Lillie Paquette/MIT
See also: MIT watches people walk through walls