This is pretty easy to do with a thermocouple like the one that Tom sells on this page
and manually entering the data into the BehmorThing
program for PCs. This is what I do.
There was a rumor that Ira (the author of BehmorThing) might be working on a USB thermocouple that would automate this in the future.
I used to have the thermocouple taped to the ceiling of the Behmor just to the right of the light, but after I took the thermocouple to work to check a microprocessor temperature issue, I now snake it along the bottom of the Behmor pointed up at the back just below the bottom heating element. I use 3M's Scotch 5413 high temperature film tape to secure the probe, tech note available here
Now that you've got temperature available, the next question is what you can do with it. From the vantage point of the two distinct areas in the Behmor that I measured temperatures, I can say that I don't have a good picture of what is going on inside the whole Behmor. I can see when the heaters are kicking on, but with the airflow and the drum, it's hard to say what the temperature the beans are seeing. I read about some Behmor enthusiast who snaked a thermocouple into the drum by drilling out the side and inserting a tube on the left to enter the drum... this is a little extreme for me. Besides, without seriously moding your Behmor, you can only adjust your profile for the next roast and not make any roasting corrections (besides maybe cracking the door or hitting cool) with the realtime information you gather.
Having said that, I do think that I've learned more about how the Behmor roasts and working with BehmorThing
understand how to better program my roasts, and I've really enjoyed looking at the data (if your that kind of person). It also gives me something to do (log the temp changes every 20 degrees during the drying and cooling ramps, and at finer increments when approaching first crack) during the roast that keeps me engaged and paying attention so I don't have to worry about the roast getting away from me.
You can see some of my temp logs in my roasts on my photobucket