A pedestrian talks on her cell phone as she walks down the street in San Francisco, Calif.
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Kai Ryssdal: Cell phones are so much a part of our lives nowadays that there might not be too many people who think about this anymore, but there's a school of thought out there that says all those cell phone signals passing so close to your brain can't possibly be good for you. Cancerous, even. The actual science on that is murky. But the San Francisco Board of Supervisors isn't taking any chances. The city's set to become the first in the country to require that retailers disclose phones' radiation levels.

Janet Babin reports from North Carolina Public Radio.

Janet Babin: Cell phone companies are required to disclose how much radiation we absorb from their devices. Just not at the store, when shoppers are all excited about a phone's new features and apps.

Soon though, San Francisco retailers will have to post radiation values, known as SAR, next to a cell phone's price tag. 1.6 is the legal limit; many smartphones are closing in on that.

Debbie Raphael is with the city's Department of the Environment.

Debbie Raphael: We feel like this is info that consumers might want to know when they're making their purchasing decision.

The industry argues the law will mislead buyers.

Joe Gregorich is with the trade group TechAmerica.

Joe Gregorich: It could create an opportunity where a consumer thinks the one with the lower SAR is safe, when that's not the case.

There's no definitive evidence that a lower SAR value is safer. Dr. Matt Ewend is chief of neurosurgery at the University of North Carolina.

Dr. Matt Ewend: The data has been very soft -- either negative or very slightly positive -- but with a lot of questions about the validity of the data.

The city's position is that inconclusive science is all the more reason for disclosure. Renee Sharp is with the Environmental Working Group and helped the city craft the new law.

Renee Sharp: It's exactly in this situation where the science is not definitive, and the science is not settled, so to speak, is when you need to have such right to know questions.

For now, San Francisco is an outlier. But the law could have wide implications for cell phone companies. Once these values are posted in stores, they're likely to go viral.

I'm Janet Babin for Marketplace.