My APRS-based temperature monitor has now worked flawlessly for half a year. APRS stands for Automatic Packet Reporting System so it can send much more than temperature data, the chief usage is really for GPS position reports.
But I just needed a temperature monitor and here are the readings for December. As one can see, there were no days with temperature above freezing. At 800 m elevation in the mountains of Telemark in Norway, this is not unexpected for this time of year and makes for good skiing!
Quanzheng TG-25AT handheld with a quarter-wave whip antenna on 144.800 MHz. Its signals reach the LD3GT digipeater at 1845 m above sea level. Although I don't have direct line of sight, the low power (1 Watt) setting is adequate as the distance is only 10 km. The APRS-beacon is an OpenTracker USB set up for transmission every 15 minutes. An external DS18S20 temperature sensor which measures the outside temperature is connected to the 1-Wire® bus of the OpenTracker USB.
Thanks to the infrastructure providers: The Tønsberg group of NRRL (LA1T) who operate the LD3GT digipeater, probably the one with the largest coverage in Southern Norway (Gaustadtoppen). Thanks also to the various operators who receive packets from LD3GT and pass them on to the internet, and thanks to aprs.fi for processing and displaying the data on their excellent web site!