I use an FM transmitter to listen to music from my iPod in the car on
a regular (daily, 1 hour) basis. What level of health risk is involved
in this level of exposure to the FM signal generated by such devices
(manufactured by Grffin, Xtrememac, Kensington etc ?

insideright...

First, let me say that I was an electronics technician in 
the U.S. Navy, and as careful as the Navy is about safety,
I never heard any negatives about the use of FM signal
injectors, which we used both as test equipment and to 
broadcast a shipwide radio station on FM frequencies, by
inputting music from tape recorders and record players
while we were out at sea, and regular FM channels were
unavailable.

Secondly, a tailored search for:

"damage * health" "fm transmitter" -"health and" -"health &"
://www.google.com/search?q=%22damage+*+health%22+%22fm+transmitter%22+-%22health+and%22+-%22health+%26%22

...produces only 12 unique results, and the majority
simply happen to have "fm transmitter" on the same page
as a phrase concerning "damage * health" with no relation
between them.

Then there is the singular description for an FM transmitter
on the alibaba global trade website, which states:

"Hertzian waves, no damage for your health"
http://beelan.en.alibaba.com/product/50116210/50528406/iPod_Accessories/FM_Transmitter_for_iPod.html


Also, we are all constantly being exposed to FM signals 
from much more powerful sources, like local FM stations,
and if this were a concern it would have long ago been
prohibited.

On the basis of my background and experience in electronics,
as well as the lack of evidence to support what would most
certainly be a widely-publicized danger to public health,
I can tell you that the use of such a device is perfectly
safe.


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the answer cannot be improved upon by way of a dialog  
established through the "Request for Clarification" process. 
 
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sublime1-ga

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Request for Answer Clarification by insideright-ga on 12 Jan 2006 12:45 PST

sublime-ga

Thank you for your answer. 

You mention that we are regularly exposed to "much more powerful
sources, like local FM stations". I'd be interested in some relative 
values - is the kind of exposure we receive on a day to day basis from
things like FM stations twice/ten times/one hundred times ??.... more
powerful than that experienced from my little FM transmitter ?

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Clarification of Answer by sublime1-ga on 12 Jan 2006 14:06 PST

insideright...

If you look at the specifications for the unit being
sold at Alibaba, you can get some idea. It's listed
as using .05A (amps) at 12V. Power (in Watts) = amps
times volts, or P = I x E. So .05A x 12V = .6 Watts.
It also indicates a broadcast range of 30m, or 32.8
yards.

Compare this to the typical wattage of an FM station,
at between 20-100,000 Watts, with a range of 40 to 70
miles. Based on wattage, a station's signal is easily
35,000 times as powerful as your little transmitter.

This discussion of radio waves and the electromagnetic
spectrum on ThinkQuest should set your mind at ease:

"In varying AM waves, the strength or height (maximum
 displacement from equilibrium) is changed. By contrast,
 FM (frequency modulation) radio waves usually have higher
 frequencies closer to those of TV transmissions. In
 varying FM waves, the frequency of the wave is changed.
 Exposure to radio waves causes no major health problems
 and is not regulated."
http://library.thinkquest.org/27930/spectrum.htm

sublime1-ga