My favorite quick self test is to check the dexterity of my hands. Assuming you don't have arthritis or some other limitation that would keep you from touching your thumb to its neighboring fingers, you can see how nimble your fingers by attempting to touch my thumb to each fingertip on that same hand. Even with hypothermia, you may be able to touch the tip of your thumb to the tip of that hand's index finger or middle finger, but if it's taking a lot of work to get your thumb and ring finger to touch, or if your thumb and pinky finger cannot touch, you are on the track to hypothermia. The science behind this may seem a little murky, but it makes sense once you think about it. Your hands and forearms are slender extremities compared to the rest of your body. When the forearm muscles get cold, they have a hard time generating finger movement. If your arms are getting cold, it's likely that the rest of your body is cold, too.