I like and use the recorder from Scanner Recorder Home Page
It's truly voice activated and has a visual, adjustable audio "squelch".
As a matter of fact I used it just last night to capture the church fire in Somers.
It continued to record the events even after I eventually went to sleep at 2AM.
From the website:
Scanner Recorder provides a switched recorder that listens to the sound coming into the audio card and if the sound is above the minimum threshold, the recorder operates. If the sound level falls below the threshold, the recorder pauses.
Since the recorder starts and stops based on what it hears, Scanner Recorder incorporates an anti-clipping feature that keeps the very beginning of the audio that breaks the squelch threshold from being clipped off. The result is that when sound is played back, there is no noticeable "click". Also the beginning of the audio event is not clipped off (like mechanical vox recorders do).
It's Freeware with no adware or nags.
Hope this helps.