The non-prescription (in US). https://www.stelo.com works just like the Dexcom G7 (a sensor you place on back of upper arm) but it does not offer an alarm for a BG low..so it is offered only for general health monitoring, not to be used by diabetics. The difference between interstitial and capillary blood can be calibrated with a Stelo and the unit saves a 24 hour trace. You can connect to a Dexcom app or something like Apple Health and save the 2 week result, and then need to recalibrate when you change the sensor. Always, always check a low reading against a glucometer. "Compression lows" during sleep are common.
Excellent User Guides at above website. Non-invasive is still in the future.