Update to: Will not count reps. correctly
Update: The developer responded to me very quickly. Basically to resolve the issue noted below I just put my phone in my pocket upside down and this seemed to work. Still got a "Slow Down" warning no matter how slow I went. Don't have anyway to strap this to my leg the way they suggest. The phone basically tracks the movement of the front part of your quadracept, up & down at an angle. So if it's on your arm or you try to hold it in your hand it won't work.
Just sent an email to the developer. The app. will not count the correct number of reps. It says Slow or Half and will not count the reps. I've tried everything with this app. and it won't work. 1 Star until they get this fixed.
P.S. I have PushupFu and CrunchFu and love them both. Neither of these have this issue. Also, you don't need the strap. When doing push ups I tap start and put my phone on the upper part of my back and it counts just fine. Same with CrunchFu, just set it on the upper part of my chest and it counts correctly. I wear a shirt and have a rubberized case so it stays in place.