One that I use is called a indoor/outdoor acu-rite thermo hygrometer. It has a probe that you can put one one side of the cage and you put the main part on the otherside. And it will give you a gradient temp and humidity from one side to the other, and the best part is there about 13 bucks at walmart. They work pretty well and are accurate. I found it in the home garden section, but if you cant find it just ask someone