Apple CEO Tim Cook has reportedly been field testing a blood sugar monitoring device attached to an Apple Watch, CNBC reports. According to a source, Cook was spotted at the Apple campus wearing a prototype glucose-tracker on the Apple Watch, pointing to Apple’s continuing efforts to add more advanced health monitoring capabilities to the wearable device. A report last month revealed that Apple has been ramping up its efforts to create a new type of sensor that could non-invasively and continuously monitor blood glucose levels. During his visit to the University of Glasgow in February, Cook obliquely shared that he had been “wearing a continuous glucose monitor for a few weeks” and had only removed it before leaving for Scotland, although he didn’t specifically mention it as an Apple initiative, but explained that it was helping him to understand how his blood sugar levels were responding to the foods he was eating, and spoke generally about Apple’s commitment to health and the struggles faced by people with diabetes.