Every outdoor sports enthusiast who is out exercising on their own needs one of these. You never know and hopefully will never need it but it's a light rubber band that gives all the info you need if you're in trouble. Clearly printed and fast post. My only problem is for males they give a one size fits all but as many a runner and cyclist will attest to,. Our arms are not the biggest and although it doesn't fall off. They could have two sizes, one for smaller wrists so it doesn't flap around. Maybe I'll have to order a ladies!
Hi Gary, if you measure your wrist, the Large is 20cm in diameter and the Medium (ladies) is 18cm. Please choose the best size, the description is just a guide ;-)