Hmm.. I wonder if we diabetics would have problems with fingerprint readers? I guess if we use the side of the finger, not so much.
As for this app, and being a photographer/general geek.. I'm dubious. Here's something I found with a quick search showing how a pulse oxymeter could be added to a smartphone:-
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3892845/
Showing some of the challenges. Smartphone cameras are designed to take pics, and as far as I know don't have the right kinds of LEDs or sensing to do this kind of thing without additional hardware.. But companies are doing (or trying to do) neat things via phones, eg:-
https://gigaom.com/2014/04/29/consu...can-tell-the-number-of-calories-in-your-food/
which doesn't seem to have launched and the Kickstater page says it's in an IP dispute.