Okay, well if you want you could stick the thermostats probe between the glass and the heat mat, or you could run to inside the cage over the heat mat. If you run it inside the cage you may need to cut a hole in the lid of your cage or improvise somehow, not sure what your setup looks like. Oh one more thing before I post this, if you do put the probe on the outside of the cage between the heat mat and the tank you may need to set it a degree higher than you normally would if the probe was inside the tank to make sure the temp inside the tank gets to the desired temp. And if you do put it inside your tank, sorry I know I said one more thing but this is very IMPORTANT, you need to make sure the snake CAN NOT move probe out of the range of the heat mat otherwise they can reach extremely dangerous temps. Because the thermostat will think the probe is on the heat mat and keep pumping power into it to make it hotter even though it has moved off the mat and this can get out of hand real quick if you don't catch it early.