Robin2, thank you!
This tool is and shall be used for legal purposes only.
Under simultaneously I mean, not at the exact same time, but rather without the need to switch the operating frequences manually - so both 433 and 315 MHz remotes shall be identified at once.
ISR = Interrupt Service Routine? I'll learn more about it.
I downloaded the existing code, so neither do I understand some things yet.
But the SD logging part is mine - I'll optimize that and try to duplicate the ISR as you have suggested.
Thank you for your time!