I'm the same. I use a Contec CMS50I purchased new on ebay as a sleep data logger. I use SleepyHead software, however I think even the windows software that com

I'm the same. I use a Contec CMS50I purchased new on ebay as a sleep data logger. I use SleepyHead software, however I think even the windows software that comes with it doesn't require a network connection. It is a pulse oximeter that tracks SpO2, pulse rate, and perfusion index. I think they are primarily sold as a low cost option for hospitals. The data format was reverse engineered not provided by the company and while I haven't compared directly I think there might be some debouncing that should be applied in some cases involving movement of the sensor (possibly their software doesn't do anything about that either). I've used it overnight maybe 30ish times and I'm not sure it will last all that long, although the blue line the display acquired at one point went away after a while. I did find that it is a good idea to wipe with rubbing alcohol each time you use it as the manual suggests. I wish there were more options.