Your issue is proximity to the sensor. NFC works from only a few cm. Beyond that you need something different. On that note, I wonder what the battery life on a sensor is in terms of swipes, as I'm pretty sure every 15 mins would give it a week or less. (I wonder if that is why some people are seeing sensor issues earlier in the 14 day life than others? Over swiping...) Technically then, introducing this kind of thing brings it far closer to a classic cgm along with the limitations that incurs.