The doctors and nurses didn’t believe Tomisa Starr was having trouble breathing. Two years ago, Starr, 61, of Sacramento, California, was in the hospital for a spike in her blood pressure.

The last time you were in the emergency room after a horrible accident involving a PVC pressure vessel, a nurse probably clipped a device called a pulse oximeter onto one of your remaining fingers.

In recent times, the demand for oximeters has soared due to the increasing need for monitoring oxygen levels at home. With a plethora of options available, it can be challenging to choose the best ...