Buy a temperature logger. They can be had for <$50.

edit: Here's one for <$25

edit2: Or for a bit more money ($150), here's a really nice one that will do 4 channels and >2000 F

Last week I found an older post of yours that got me thinking about temperature data loggers. Of course I wanted to see how cheap of devices there are out there. I found this which is kind of cool since there is a display, it's a recorder but no Bluetooth. Elitech RC-5 USB Temperature Data logger Recorder 32000 Points High Accuracy https://www.amazon.com/dp/B00MQSCZF2/ref=cm_sw_r_cp_apa_Jri.BbZGVRK0S.

I like that watch that was posted in this thread, I wonder if there is an affordable watch that has temperature and compass features and also records data over time?