I know this'll sound like my usual gripe. I wouldn't carry one in the outdoors no mater how good it was, unless you are also going to carry oxygen. Monitoring something that you cant do anything about will only cause distraction and stress. I also wouldn't use a cheap one no matter what. There is always a margin of error, usually +/-2% with the expensive devices, I dread to think what it would be in the cheap ones. I often find with people who have been lying in the outdoors you cant get a reading due to them being cold and peripherally shut down. The casualties colour will tell you all you need to know about their condition. Sorry to be negative, but you really don't need this stuff for outdoor/bushcraft first aid.