Bob: The key will tell the radio what system to listen too much like a scanner. Otherwise it does not know what system to monitor. Good Luck Sir. To be clear, you are asking questions that your friend should be able to answer. He/She knows a key will be needed and if they didn't advise that I would make sure and clearly ask that question. ALL the post above from me were merely educational, do as you please, just be aware of what you are getting into with a XTS radio monitoring a system.