Amazon.com: FaceLake ® FL400 Pulse Oximeter with Carrying …

Place finger in device and press power button. After scanning, a reading will be displayed; the left number is the SPO2 (blood oxygen saturation) level and the right number is the pulse rate. … I would have thought it works by insertion, but no. The heart rate monitor works by a bar scale, not a graph, so that’as non linear, too. The other …

https://www.amazon.com/BESTHING-Wireless-Charger-10W-tf67/dp/B01MQY43YD