The easiest way to tell if you are transmitting is to look at the current that the module is drawing. Please take a look at our datasheet
to get an idea of the TX currents for the various modules. When the module is transmitting you should expect current draw ~44mA - 150mA depending on if you are using a low power (ZICM35xSP0) or high power (ZICM35xSP2) EM35x Mini Module.
You will want to make sure to follow our software design guideline
and ETSI, IC, and FCC power restriction that our listed in our datasheet