Many of the low priced smart watches have fake sensors for reading heart rate. They will just have a flashing green or red led. For proper instrumentation, You need a reg led, Ir led and a photodiode to read blood flow on the wrist when wearing the watch. One test is not to wear the watch and place it on a toilet paper roll and see if it gets a reading. It should not. To help make the fake reading seem real, software in the watch will use step motion rates to increase the reading when your exercising. Has anyone done a study to list the fake ones? I myself saw a Amazfit watch for less than 20$ at Amazon and wonder if any of the Amasfits can be fake at such a low price. I would have to see the sensor and run a test. I guess if I determine its fake, I can always return the watch. All I want is a simple BPM and O2 sensing tracker for a reasonable price without being fooled. The sensor ic for these watches are not expensive at all. On Aliexpress you can get a module with a MAX30100 sensor for a dollar. I guess if you eliminate a dollar per watch for 1,000,000 sold, you can save a million. Buyer beware.