Reply to Live music - Key detection Software

Hey!

Does anybody knows any software or app (would be better) able to recognize the track key without scanning the mp3 file, I mean, just receiving the audio input on the microphone (leptop/Iphone/Android)?
The intention is to know the key beeing played by other dj before I start up my djset (back-to-back).

Thanks a lot,

Cheers