Search Reddit, lots of doctors and med students discussing which of the cheap ones work. Nearly all are sold out though. I bought this one last night based on

Search Reddit, lots of doctors and med students discussing which of the cheap ones work. Nearly all are sold out though. I bought this one last night based on Reddit feedback for $35 but it's already sold out: https://www.amazon.com/gp/product/B01HSAG8BE/ref=ppx_yo_dt_b_asin_title_o00_s00 https://www.amazon.com/gp/product/B01HSAG8BE/ref=ppx_yo_dt_b... If you've got $300 to spare, this one is allegedly FDA approved: https://www.masimopersonalhealth.com/products/mightysat-fingertip-pulse-oximeter-with-bluetooth-le-rrp-pvi https://www.masimopersonalhealth.com/products/mightysat-fing...