I purchased the Sweat Patch in December and used one for a one hour run on a 55 degree day in North Carolina. It and the app worked as directions explained.
I used the second patch for a one hour run today, July 8, when it was 77 degrees and 95% humidity at 6 am, also in North Carolina. The patch lit up completely orange while I was running and with a purple stripe down the right side. When I stopped running, most of the patch had returned to white, with a small amount of orange at the bottom of the patch as well as the remaining purple stripe. I tried to scan it with the app on my phone eight times, but it continued to fail. I tried all the help suggestions: brighter light, scanning straight on, etc. No results and a waste of money on this patch.