Any simple VAD implementation?

I'm looking for some C/C++ code for VAD (Voice Activity Detection).

Basically, my application is reading PCM frames from the device. I would like to know when the user is talking. I'm not looking for any speech recognition algorithm but only for voice detection.

I would like to know when the user is talking and when he finishes:

bool isVAD(short* pcm,size_t count);