One of the linked articles has some more technical details on how non-invasive blood sugar measurement works (for the GlucoWise device currently in development)

One of the linked articles has some more technical details on how non-invasive blood sugar measurement works (for the GlucoWise device currently in development): The glucose levels are extracted by a non-invasive technique which transmits low-power radio waves through a section of the human body, such as the area between the thumb and forefinger or the earlobe. These areas have adequate blood supply and are thin enough for waves to pass through the tissue. These signals are then received by a sensor on the opposite side of the GlucoWise device, where the data about the characteristics of the blood within the flesh are collected and analysed. The other non-invasive technique that has received a lot of press is, of course, Google/Novartis' contact lens. That device measures blood sugar from tears. Most other blood sugar measurement systems require either blood draws from a pin prick or a sensor attached to your body that measures sugar content in the subcutaneous fluid as a proxy for blood sugar.