Occasionally while listening to ATC, I hear a beeping in the background of their transmission. My suspicion is it's a traffic conflict alert since the beeping is usually followed with a traffic alert to a pilot. But other times I've heard the beeping without a traffic alert.

Here is a short snippet from today of Norcal Approach at KOAK demonstrating the beeping heard in the background: https://vocaroo.com/lD93L8D5lJ3


2 Answers 2


I can't identify the specific sound, but - just like in a cockpit - there are several different audible alerts in a control tower/control centre. Just to list a few:

  • Conflict alert, as suggested in the comments
  • Various other radar based safety nets (MSAW, MTCD, DUPE etc.)
  • Strip printer printing a strip (not an alert as such, but the sound is quite noticable)
  • Phone ringing (typically a tower has several different phones, possibly with different ringers)
  • Fault indication on a runway light/navigation aid
  • Change in status (on/off) of ILS equipment (localiser, glideslope, DME)
  • Crash alarm, when activated by the controller
  • Microwave/toaster timer! (at least in smaller towers without a separate kitchen or break room)
  • Several others, depending on the local equipment

It may be a bit startling when you hear something on the radio that sounds like some sort of alarm, but you shouldn't be worried. The sound can signify many different things and it does not necessarily indicate anything dangerous.

  • 2
    $\begingroup$ Anecdotal comment: The first time I used our toaster at work it almost scared my to death with an extremely loud beeping as the timer ran out. $\endgroup$ Commented Jan 20, 2020 at 10:02
  • $\begingroup$ Makes me think of the Pop Tart scene in Pulp Fiction :) $\endgroup$
    – TomMcW
    Commented Jan 21, 2020 at 18:34
  • $\begingroup$ To me that definitely sounds like STARS' initial CA aural alarm. My thinking is strengthened by the traffic call (eleven o'clock, mile and a half). The "oh shoot" alarm has the same tone but faster. $\endgroup$
    – randomhead
    Commented Feb 1, 2021 at 2:31

It could be a traffic alert (or low altitude alert, or 7700) on a different sector. Many controllers sit in a room together at neighboring scopes; I've occasionally heard a couple of seconds of conversation and other background noises.


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