Gotcha. If I wanted to know that from a data perspective, I'd get a little keychain one like this:
http://www.rei.com/product/408047/r...-4080470000&CAWELAID=120217890000777242&lsft=
The stick on ones elkyinzer refers to are good for homebrewing but shouldn't get wet.
Do you really want to know how cold it is???
I usually just look at my water bottle/bladder in the morning - few ice crystals = its a titty bit nipply, slush = wish I brought the wood burning stove, frozen solid = its gonna be a long day.