They are activated by stomach acid and are powered much like 'potato batteries', in which two different metals generate a current when inserted into the vegetable.
Each sensor contains a tiny amount of copper and magnesium, says Thompson. “If you swallow one of these devices, you are the potato that creates a voltage, and we use that to power the device that creates the signal”.
The digital signal, he adds, cannot be detected except by a device that attaches to the patient’s skin, much like a bandage, and also monitors heart rate, respiration and temperature, showing how the patient responds to the medication. These data can then be relayed to a patient’s mobile telephone and shared with whomever the patient chooses.