This is a tough issue to describe. 
My friend and I both had VOX turned on with our Sena SMH-10 and 10R headsets respectively. When my VOX is activated, I hear a low-pitch beep and he gets an alert that I'm wishing to connect. We're connected. That seems to work great. Love it.

On the way out on a long trip, it worked great.  But the other day on the way home, my XM radio listening from my Garmin 665 would suddenly be interrupted by my friend, no alert or intercom request or anything.  He was just suddenly there.  When this happened, neither of us got an alert or any notification that intercom was being requested. We were just suddenly connected and my XM radio listening would suddenly end; replaced by his ambient helmet noise. So he would have to disconnect from me to end the connection (so I could go back to listening to my XM radio)

Thinking it was his VOX falsing, he turned his VOX OFF, mine was left ON. (it's not easy to manipulate the 10R controls with gloved fingers)  It still happened frequently.  

If it happened once in a while, no problem. But it happened every five or 10 minutes as we rode.   I finally gave up listening to a program on my XM radio and listened to his helmet noise; the intercom was interrupting so often.  My VOX sensitivity is turned down to where I have to yell to get it to trip in; so I didn't think it was because of over-sensitivity.  

Anyone else experience this?  Any ideas or clues as to why this was happening? I haven't updated the 10R firmware yet. It was released the morning we started on this trip.