The payload was the 4 digit code, it was a large tornado warning siren. The msg was "be loud". I lived 300 yards from it, and had a dad with a police scanner. I noticed a pattern after a while... Saturday's they ran some test of the system...4 digits at noon on the radio and a blasting sound would follow
He likely means emergency sirens - I also had some friends I'd hang out with as a teenager who figured this out as well.
As far as I'm aware this is still the case - but some sites are now encrypted radio. From what I've heard though, that encryption may not be the best implemented in all areas.
It was pretty recently someone set off the civil warning sirens in I believe a city in Texas via this method as well.
I'd like to say this was a one off experience in my "exploring civil infrastructure" days - but it's really just barely scraping the surface. The state of these systems makes you realize how much civilization is held together with tin cans and duct tape, and how much marketing fluff there truly is out there inspiring false confidence.
Smart system, really. Very simple to install/maintain and very simple to have a robust transmitter infrastructure around.
If you just substitute your 4-digit code for a longer, say, 64, digit one with some time-based component, and perhaps shift the required frequency too based on time, you actually end up with a very robust very simple system.
I disagree. The frequency hopping would make it harder for a signal jammer to prevent a legitimate transmission. If you can't predict the frequency on which the transmission is being listened for, you'd need to jam a broader spectrum, needing much more power to perform the attack.
