Want To Detect Sound
Try MixMonitor. Land the call to a local channel and answer it. This code will record the silence as well.
exten => _X.,1,MixMonitor()
exten => _X.,n,Dial(Local/100@context1)
[context1]
exten => _X.,1,Answer()
exten => _X.,n,Dial(SIP/${EXTEN}