i use the acurite 00891 model which measures an "in" temp and "out" temp along with humidity so essentially killin' three birds with one stone lol.

i place the unit itself on the cool side to get a measurement of the ambient or "cool side" temps and then run the probe to the "warm" side to get a read out from there and while its in the cool side it gives me a readout of the humidity as well like the pics i have posted below.