Continuous glucose monitors are not significantly larger than a watch. See pictures here https://www.dexcom.com/g6-cgm-system https://www.dexcom.com/g6-cgm-sys

Continuous glucose monitors are not significantly larger than a watch. See pictures here https://www.dexcom.com/g6-cgm-system https://www.dexcom.com/g6-cgm-system and here https://www.freestylelibre.us/ https://www.freestylelibre.us/ They are also more precise than it sounds like you think they are. I think that all current models require some calibration every once in a way (maybe every few days). Also, there is a lag, but it is fairly predictable and for a lot of potential use cases the lag is not an issue. Continuous glucose (and lactate and maybe cortisol) monitors are not like Theranos.