The PA system functions as that; at least, I think it does. The TSA, Airport Police, Gate Agents, Ticket Counter Attendants, etc. all have access to the PA system I believe. I know this because of all the “Airport Security Alert! Unattended baggage is dangerous! Keep watch over your baggage at all times. Report unattended baggage by notifying the TSA, or airport police, blah blah blah” announcements, plus I’ve heard the TSA calling people back to the checkpoint to claim the stuff they might’ve accidentally lost/left there, that sort of thing. Since the PA system covers more area than the horns (or even speakers if applicable) and is more easily accessible to airport personnel, etc. then I think it is okay. Plus the portions that now have TrueAlerts and TrueAlertES’s at the renovated parts used to have System Sensor MA/SS devices, and since the airport is pre-9/11 I don’t think everything applies…but I could be wrong, although I’ve seen plenty of airports with horn/strobes before too. But I have seen plenty airports that use speaker/strobes too, so I don’t really know the answer to that, but I think it probably depends on the type of job, the type of airport, and ultimately it’s likely a money saving decision.