VAD从侦听模式切换到说话模式

I am attempting to turn my four-wire apartment buzzer into a VOIP phone using a raspberry pi and a custom circuit. The problem is that two way communication is not supported. I can either be listening or speaking. I want to use a standard SIP setup with asterisk, but do VAD on the sound output of the raspberry pi in order to send a digital signal switching the intercom to "speak mode" whenever there is a voice on the audio output. Is there any pre-existing c function or include that listens to the ALSA mixer and throws a 1 for speech and a 0 for absence of speech with sufficiently low latency to be used in this walkie-talkie like system?I am attempting to turn my four-wire apartment