Bests & Worsts Reviews from Amazon

The manufacturer says that it is accurate to ±2% on O2 and ±2 beats on pulse. I run with a rescue squad and checked against our $300 pulse Ox. It is within tollerances. It works fine while walking or mild exercise--like a stationary bike. But it will come off of your finger if you try to use it during vigorous exercise. It works better on the middle finger than the first and if you have long nails it may read inaccurately or marginally.