You've probably read somewhere that your radio allows you to set up a more private channel using something called "privacy line" or "sub-channel". Take
In the days of yore before the widespread use of cellphone devices radio was the King of Communication. With so many users on the air interference became an obstacle. In the 1969s CTCSS became available. Texas instruments marketed as P.L. (Privacy Line) and the name stuck. CTCSS or Continuous Tone Coded Squelch System sends out a subaudible tone along with your voice. The receiver at the other end "hears" the tone and allows your message to be heard!
Provided that the receiver is listening for the correct tone that is. If another signal is sent but with the wrong tone, your receiver will hear the tone but take no action and thus you will not be able to hear the Communication.
Now the bad news! Squelch is to inhibit or suppress something. In this case radio Communications without the proper tone. If you were to transmit with a tone to your friend and someone was located in an area to intercept your signals you're in the clear right because you have to have the same code to hear?? No, and that's why I'm writing this post. You and your friends have inhibited or suppressed signals without the correct tone, not the random listeners, they kept their receivers uninhibited and still receiving all signals, with or without codes let alone correct ones.
Don't be fooled by the hype, just because YOU can't hear everything going around you doesn't mean you're all alone in the radio world.
Hope this was somewhat helpful.
Note: DCS just means digital coded squelch, instead of a tone, a digital code is sent.