andriej:
I might try on desktop PC, but I dont want to burn it so I have to be sure that those resistors are ok.The yellow data wire is going straight to RF-transmitter module (it has a visible antenna also).
For a 5V input the 39K/10K you refer to gives a 1.02V output that should be okay. If you prefer to be cautious then try a 48K/10K that will drop the output to about 0.86V
Sounds like the yellow data wire may be a place to tap in, depends how smart the transmitter is as to if the data is raw transmitter on/off or a micro interface. Can you measure voltage when the unit transmits to be sure voltage is 0-5V range.