We don’t, the latest commercial technology consists of disposable sensors that require a probe to penetrate the skin. Whoever brings something non-invasive (and reusable) to market will be raking it in whether they’re apple or not.
There's also an alternative using radiofrequency: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4641327/
That product doesn't exist yet, the video on the home page is 18 months old so it's probably not feasible / accurate.