You don't need to worry about data storage even if your phone isn't around. It supports sync with Apple Health. (The APP reminder works only when your phone stayed in Dashboard and not locked). WIRELESS:Bluetooth.
This oximeter is easy to set up and use. Please remember to read the instuctions before using, I didn't and I thought it wasn't working correctly, but after checking, all is well. I would recommend this product if you want or need to monitor your blood/oxygen levels while you sleep or any other time.
The device does a good job monitoring blood-oxygen. It is, by far, the best for over-night use. However, it is short lived, and the company does not honor their 1 year warrantee. I have used at least 25 and most last less than a year. I have never had one replaced under the warrantee.