This "Reality Check" needs a reality check of its own.

See, "Radiation" is an all-encompassing term. Nuclear radiation is not the same as radiation from a TV or PC.

PCs emit RF, while TVs emit small amounts of X-Rays.

OTOH, Nuclear materials give off alpha, beta and gamma radiation.

I'm reasonably certain a nuclear detection device is not going to respond to PC "radiation". It _might_ react to an old radium dial, as well as some relatively new watches which contain tritium.

As a nuclear engineer, the simple answer to you question about whether we are surrounded by many sources of radiation, is "YES." Although I have had many discussions with environmentalists who seem to think that the only radioactive substances in existence are those created by man (so radioactivity = man-made = bad). However, for the record, TVs and PCs emit non-ionizing radiation (e.g., radio-frequency radiation), not ionizing radiation (e.g., gamma, beta, neutron or alpha). I do carry around a microrem Geiger-Mueller device, in part just for kicks, but also because I would be able to distinguish the natural background radiation from a strong source; I agree that unknowledgeable observers would have a lot of false alarms, although getting people to better understand radioactivity and radiation is a good thing - hopefully will dispel the hollywood fear-mongering nonsense which permeates everyone's thinking on those subjects.

An even more pervasive source of radiation is granite that is used in buildings, counter tops, etc. It contains tiny but very detectable amounts of uranium and other rad sources. A typical granite building emits more radiation than a nuclear power plant does.

Mr. Schwartz,

In fact, the longer the system runs, the more false positives are eliminated. And the more the constellation of detection nodes grows, the higher the resolution of information.

Right now there is an infinite sea of ignorance on where the nuclear threats may be. So, trucks and teams from the government wander our cities looking for a needle in a hay stack. But with a constellation of phone detectors, the hotspots unknown to the system could be targeted by the million dollar detection trucks. Today, those trucks can only hope to 'get lucky'. And mathmatics says they have little hope.

As for the mob shaking their fist at the individual, there would be no such person. One phone doesn't set off an alarm - data in a computer gathered from many phones creates a mathmatical alarm. The individual is part of the swarm and has no idea of their contribution or lack of it.

Thank you for stoking discussion on this topic.
We have no civil defense against nuclear terrorism as of today which comprehensively covers a city.
This is the only readily achieveable way to do it. It is absolutely necessary that we do it.