I would guess a good percentage of the Slashdot community worked in college radio (seems the nerdly thing to do). But for those who didn't, let me tell you about the old Emergency Broadcast System...
The radio station DJs were taught to take the EBS equipment in the studio very seriously. Our studio was located in an actual fallout shelter... thick concrete walls and no windows... we even had the cool fallout shelter sign outside the door. If one needed to take shelter from nuclear fallout there was plenty of vinyl to keep you company but not much else. The space was tiny.
We had to know the procedures for handling both an automatic EBS test (triggered at random times) and a manual test which we performed weekly. More importantly we had to know the procedure in the event of an actual emergency.
The automatic test would just happen randomly in the middle of your show any time of day or night (I don't recall how frequently this happened). My normal broadcast would get hijacked by the EBS equipment (which was connected to the transmitter) and the alert system would begin broadcasting the test message, followed by the tone, followed by closing message. After this test we had to manually reset the EBS equipment by pressing a button (or power cycling the damned thing) in order to regain control of the local broadcast from the studio.
The manual test was performed weekly by the DJs (we did it at 6AM on Monday). I'd play a cart with the opening message, "This is a test..." and then I'd have to press a button on the EBS to play the tone. It tested the system's ability to interrupt my broadcast. At the end of the tone I hit the reset (or as previously mentioned, power cycled it) and then played a second cart with the closing message "this concludes a test of the Emergency Broadcast System..."
In both test cases I had to log the time of the test (or risk going to FCC, bang you in the ass, prison??).
If the message turned out NOT to be a test I was to tear open the special red envelope hanging by the equipment. Sadly, I never got to do this. The envelope contained a codeword. One would compare the code transmitted to the EBS with the code in the envelope. If it was a match there were further instructions in the envelope which remain a mystery to me (although someone once told me that since we were a small station we would likely be instructed to shut down our transmitter while stations with more kilowatts would be instructed to boost their signal).