With Apple's Silence Unknown Caller feature, if a call that is not in your contacts reaches out to you, it will automatically be prevented from ringing. This causes the missed call notification to appear on your phone. Every time this notification goes off, you will know that you've received a call from an unknown number and RoboKiller is screening it for you! (Call screening is only available with Advanced Blocking). 

If you are on iOS 14

Be sure to change your incoming call display to ‘Full Screen’. To do so, please open your Settings > Phone > Incoming Calls > Select ‘Full Screen’

RoboKiller's call screener:

• Informs the caller that the number they called is using RoboKiller 
• Asks the caller for their first and last name
• Asks the caller for the purpose of the call

Once the call is screened, and RoboKiller does not detect it as a Spam Call, you will receive the caller's name and reason for calling.