How to interpret wireless communication signals after being recorded?
You have to find the protocol being used somehow.  Preferably you find a document that tells you outright.  You might be able to reverse engineer it, but less likely for someone that has to ask about basic decoding here.  You say the protocol is standard, so you obviously know something about it.  If it's truly standard, you should be able to look up the standard.

Additionally for your scheme to work, the radio you use has to demodulate the RF signal according to this standard, and the resulting baseband signal has to be in the audio range, perhaps less depending on the radio.  For example, if the radio is doing AM demodulation then this isn't going to work if the device is using frequency shift keying.  Also, if the device is transmitting data at 30Kbits/s it also isn't going to work if it's a normal audio radio.

Added:

I just noticed you plan on plugging the radio output into the microphone input of the computer.  That will most likely overdrive the microphone input amp.  You should plug the radio into the "line in" jack instead of the microphone in jack.  Most sound cards (or motherboards) these days have both choices.