The spec sheet for the thermometer would probably have all the info needed to figure out how to use it, but those can be confusing sometimes. If we had some more information (make, model, part number, link to a spec sheet, etc), we could probably help better.
Without that... i would suggest doing a few tests. Start with the thing at room temperature and get a recording of what it sends like you did above. Then stick it in the fridge, let it get acclimated, then get another recording. Transition to the freezer, and get a third recording. For all of these recordings, make sure you also record the temperature at the time of the recording, using another thermometer with a simple digital readout if needed.
You should be able to compare those three recordings and figure out the differences - how does the transmission pattern change as the device is in colder environments? You should be able to plot those changes against the temperature, and see some sort of trend. If the trend isn't linear, you'd probably want more data points at other temperatures to be sure you understand it correctly. All in all, it sounds like a pretty fun little experiment
