After a recent visit to the emergency room because I was having trouble breathing I was told that I my blood oxygen levels were too low.  It was recommended to me that I get a pulse oximeter to monitor my levels at home. My doctor told me the best brand to get was Nonin.  I decided on the Onyx 9500 by Nonin.  I liked the features it offered, its ease of use and readability.  Ever since I have been monitoring my use at home I have been able to much better control my breathing issues and keep my oxygen levels within a more acceptable range.