I meant to update this thread over the weekend but forgot. Anyway, I just ending up taking it back to wallyworld and exchanging it for a new one. Gotta love walmart's exchange policy. Here's how it went:
I walk up to the customer service counter. There are two large women with their eyes half shut, about to fall asleep at any moment. I have the thermometer in a grocery sack. No receipt, no package, not even the walmart bag.
Me: Hey this thermometer quit working all of a sudden. I'm gonna go ahead and get a new one to exchange it with ok?
Large lazy customer service lady: What is that?
Me: A digital thermostat.
LLCSL: *SIGH* Umm..ok but I can't let you have the package for the new one.
Me: OK. Thanks.
So the new one works fine. Must have just been a defective unit.