The Microsoft Band has an Ultraviolet senor and it will display on the screen the current UV level but that is about as far as it goes but there is a new app for the Microsoft Band that adds some great new functionality. Band Sunburn for Windows Phone will not only measure the UV level but it will also alert you when the radiation level approaches your threshold saving you getting burnt.
There is a dial on the Windows Phone app where you can set the alert levels and then it will go off and monitor the UV levels. Due to the way Windows Phone works the phone display says on as apps can’t run under the lock screen and I guess it will be using extra battery on the phone but if it saves you getting a painful sunburn it’s an app worth downloading. It’s free from the Windows Phone Store.