Using this code for Garmin, you can estimate without the need to purchase the sensor. The core temperature.
deploy If you do not want to go through the IQ Store you can deploy directly on the device, inside the folder garmin/apps folder of the device.
Or you can also generate .prg files and copy them directly to your computer. in the garmin/apps folder of the device.
Compatible devices To find out which devices are compatible, open the manifest.xml file
Parameters & constants If you have records of your basal temperature, you can change the value of the cts constant=36 to your value in degrees Celsius.