When the iPhone first came out, the way you measured your heart rate was by putting your finger over the camera on the back of the phone.
Right, but that's why the products become commoditized. The inventors get an early burst of success and easy money, but everyone else figures out how to make similar products very quickly.
Even smartphones are commoditized. The iPhone and the Samsung phones are the rare examples of commodity hardware that can beat the competition on the strength of their software experiences. The other companies are fighting tooth and nail in a textbook example of a commoditized market where the profits are difficult to eke out.
Actually, no. Pulse-oximeters were always quite cheap. Also, Casio had heart rate (although not continuous) monitors on some of their watches for many years.