[21twelve]

Interesting. I was thinking it would be easier to have the cell-phone providers on speed dial, but what if the private firms balk at shutting that whole sector down?

And then it would also interfere with emergency response.

But having little black boxes near critical places (airports, train stations, stadiums, etc.) they could maybe jam the signals going to a remote detonation bomb without shutting everything down. Of course then you need to hope they cover most things.

[21twelve]

Oh - the other thing would be radiation monitors that would alert the authorities.

[A CA Guy]

President drove by my place a few times in the motorcade.
One of the cars in the group had what looked like a giant dark thimble on the roof.

I'll bet that was a jammer to prevent someone from throwing a backpack of explosives and using an electronic device to detonate it.