Receiving temperature and hygrometry from a LaCrosse WSTX35DTH 868MHz sensor


I have a StarMeteo weather station with an outdoor sensor that transmits temperature and hygrometry every 5 to 10 seconds.
StarMeteo is French based company targeting only the French market, but their hardware is made by LaCrosse technology and so we can find some technical details in their web pages.
For instance, here is the page for the sensor I have: TX35DTH-IT+
It’s extremely similar to the TX29DTH-IT+ one, the only difference being the “Star Meteo” logo printed on the “French only” TX35 sensor.

All I could gather from their website and user manuals is that it is using the “IT+” technology to communicate. But from the device itself, I can see it is communicating on the 868MHz band for which I could use a RFLink sensor for instance.

When used in conjunction with the weather station, here is the protocol for them to communicate:

  1. Remove batteries in both sensor and station and wait at least 30 seconds
  2. Place batteries in outdoor sensor
  3. Place batteries in weather station, within 1 minute of powering up the sensor
  4. If the weather station does not receive values from the sensor, start over

The documentation suggests that the communication is “encrypted” and that the above protocol is required for both items to exchange a “key” in order to understand each other properly.

Does this kind of device sound familiar to any of you?
Is there any hope for me to receive its data?

I’ll send a request to the manufacturer for protocol details, but I doubt they will answer.