The topic has been touched on, but not really outlined.
Yes, if someone lives in a climate where 20 degrees F is considered cold, then urine would make an"acceptable" solution for a frozen door (I say door because, around here, a frozen door is much more common than a frozen lock). The fact that urine is a solution means that it does freeze at a slightly lower temperature than pure water.
However, there are parts where -20 can be considered a nice day in January if the sun is shining and the wind is calm. I must offer a very strict warning against using this method if anyone lives in an area of such extreme. It is actually common knowledge around here: nothing warm to de-ice my locks. Even the salt-level in urine won’t keep it from freezing. Once upon a time when the mercury had dipped to -47, I actually had the misfortune of having to pee outside. I watched my urine gather like a stalagmite on the ground. Yes, urine does freeze. And, yes, it will freeze before a person’s hand has time to put the key in the lock. Thank God for that, too, because otherwise the key would freeze in the lock.