I found a very odd number.
Recording is attached. Its like a siren tone, here is a desciption of the sound:
the following is repeated 10 times: 620hz for 240ms, then 30ms silence, then 430hz at -2db in relation to previous tone for 240ms, then 30ms silence
after that there is a Click (and small LC ringdown) then 200ms silence and then another click (and small LC ringdown), then the whole thing repeats again
I sat on it a couple minutes listening, and it never did anything else.
I figured out it must not be anything very sensitive because it doesn't respond to DTMF, so here is the number: 301-999-9999
Turns out that there are lots of numbers in the 999 exchange that respond this way, while some such as 9900 go to a normal NIS message. I know these are based out of the hagerstown maryland CO, and being in the same LATA but a different CO and attempting to dial one on a pots line causes a normal NIS message when attempting to call a number that is usually the odd siren tone.
So WTF is this?