Read the forum guidelines
I am hoping that I am wrong about the single-ring "alert." I sometimes get 10 or 15 junk calls per day, and having each and every one ring my phone a single time would be a continued annoyance. If it's true, then I see no point in implementing Nomorobo and will continue to seek out a call-blocking service or method that really works.
You'd have to get a standalone call-blocker with first-ring suppression. I haven't been shopping for blockers in a while so can't readily recommend one.
As I was fed up with the daily onslaught of robo and junk calls, as well as providers' inability to stop them, and because we needed new phones anyway, I purchased the AT&T CL82407 DECT 6.0 system of 4 phones and base for $79.99. The system has a Smart Call Blocker built in that requires anyone NOT in your directory or whitelist to press '1' once to get thru. You can then whitelist them. So far it has stopped the phone beggars dead in their tracks. Not a single robocall thus far. And NO one-time ring at all. Problem solved.
That's a nice feature. If you have legit robocalls...dentist or doctor reminders for appointments, whitelist them as well.