Cheap Temperature Monitor for Glass Window

Found a cheap way to monitor your case temperature.Go down to your local pet shop and purchase a fish tank stick-on temp gauge,there work fine and cost about four or five bucks. Stick it to your glass side window. Works fine for me ,cheap and pretty on the money.

I'm wondering how fast the temp changes on one of those? That seems like a pretty good idea...

Yes, but these thermometers are usually not so accurate (mean +-2°C)