There are non invasive sugar detectors, which is capable of detect sugar from saliva, sweat. You can look into them

You can also use non-invasive optical sensors, through the skin.

I am also interested in this topic. Who did you hear from that Bio Impedance is one such technique for finding Blood Sugar levels?

Bio Impedance is the technique to find the different analytical parameters related to human body. In this technique, a potential is applied to body through electrodes which will change our body impedance, that reveal different parameters such as glucose level, RBC, WBC and Blood Pressure etc.

Dear colleagues, please forget all totally none-invasive methods! Most of them are more voodoo science not worth any serious discussions. Several years ago such an optical device was even sold on one of the greatest medical exhibition (Medica, Duesseldorf). The costumer got not any result but the offer to be part of a worldwide study to find the correlation between a very small change in the spectra and the individual glucose concentration. Never was an interlaboratory comparison test performed – the only argument to belief the statements!! All other body liquids have not a constant relationship to the blood value, thus they are worthless! Every year beginners or betrayers try to offer the ideal solution. Having worked in this area for over 40 years I know the situation to some extend,

I respect the 40 years experience of Professor Karl Cammann but I'm not sure that we should reject all non-invasive solutions. I have no competence in voodoo but it may be possible that the combination of signal processing, however small, and optical methods or impedance measurement or composition of sweat, would measure glucose. It should be kept in mind that this may not be accurate but only indicative. Without the experience of Professor KC without being a beginner, I recommend to young researchers do not hesitate to look into ways that seem improbable today.

Yes Sir, I am also working in this field.