Coming from my phreak box knowledge, the box that applies to this type of thing is called the Chrome Box.

All this box consists of is a strobe light tuned exactly to the frequency of the strobe light on the light bars of cop cars and ambulances.

In bigger cities, they may use a system called OptiCom. All you need to trigger this system, is the frequency used and something to send that frequency to the receiver box. Most fire stations, if you go into them and ask for it and say you're doing a report on them will give it to you. All you need to do is fix the frequency transmitter to that specific frequency and you have your freedom from waiting.