You might think your cell phone is safe when it’s turned off. It turns out it’s not.

You might think that the further you are from someone using a cell phone, the less exposed you are to the cell phone’s radiation. It turns out you’re not.

A cell phone, and especially a smart phone, is always figuring out where it’s located. That’s because it gets its signal from the closest antenna. The system of antennas defines the cells that form the communications network in which cell phones swim. As a cell phone moves from one cell to the next, it sends and receives a signal from the new antenna serving it.

The faster that you and your cell phone are moving, the more frequently you and it change cells, and the more frequently your cell phone calls out its little where-am-I signal. The signal, of course, consists of a blast of radiation—even if your cell phone is in standby mode.

Of course, if you’re not moving, your cell phone isn’t looking quite so hard, and so you’re less exposed. But if you’re on your bicycle or on the bus or on the train or, God forbid, in your car, your cell phone is searching, searching, searching.

At the same time, while it’s searching, searching, searching it’s irradiating you and the people around you. And you who are without a cell phone but are surrounded by cell phone users are exposed too.

Experts and informed citizens who love this technology will point out that this really isn’t a problem because of the inverse square law: as distance increases between a source of radiofrequency radiation and you, the intensity of the signal (and presumably the intensity of its health effects) decreases rapidly.

There are two problems with this.

First, low dose exposures to non-ionizing radiation are being found to have larger than expected biological and health effects. The standard way to measure toxicity is to find an exposure at which the toxin has no effect. It’s then assumed that lower doses are safe. This is referred to as a linear dose-response curve. However, there are well known substances that are harmful at high doses and low doses but benign or even beneficial at doses in between.

This is a U-shaped dose-response curve. Salt is an example.

This happens to be a growing problem for toxicology in general, but the common thinking and much of the expert thinking hasn’t caught up with the science. An example of the health effect of a very low dose of cell phone radiation is the breakdown of the blood-brain barrier, a barrier that protects the brain from toxins.

The second problem with distance making things safe is that it depends on where you are. If you’re in a car or bus or train or elevator or other metal box, those where-am-I signals from cell phones don’t diminish with distance. That’s because metal reflects close to 100% of the signal. Wherever you are in the metal box is as intense as being right next to the cell phone. In fact, there will be hot spots in the box that are worse than being right next to the cell phone.

In the introduction to the article about this effect, Japanese researchers observe that “A typical objection to concerns about reflected microwaves was presented in the magazine New Scientist, in which a specialist conceded that microwaves would bounce around the inside of carriages and boost field levels. However, he claimed, “the increase should be minimal, because power drops off a short distance away from each phone”. It seems that specialists with this viewpoint are not familiar with the basics of partial differential equations.”

That’s an insult. It says that these experts don’t know the basic math of their profession. The same can be said of New Scientist, which never met a technology it didn’t like and gets editorially cranky when anyone has doubts about the value of new gizmos.

What we are told about a cell phone’s safe distance is a good example of how we’re put in harms way.

I recently had an exchange with the owner of an Internet service who delivers broadband using radiofrequency signals—think of it as area wide WiFi. He challenged me to produce one placebo-controlled study that showed an effect from exposure to radiofrequency radiation. I sent him two survey articles that discussed dozens of such studies. I never heard back from him.

It would be one thing if this was an honest disagreement between experts and citizens who see no harm and people like me who see a public health disaster brewing. But what I’ve both seen and experienced is some of the worst kind of behavior: from ridicule to ruined careers.

But then I think that, if this were 1950, secondhand smoke would be a joke. It took a long time and some crafty, decentralized politics to get where we are today.

And then I think that, even today, a fifth of people smoke—with the heaviest use among young people 18 to 30.

So there’s hope—of a sort.