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A BOMB has reduced a shopping mall to rubble, leaving rescue workers
desperate to know if anyone inside is still alive. Thanks to a remarkable
discovery at Bell Labs in New Jersey, they could one day find out simply by
calling the cellphone of someone lying unconscious inside. That’s because the
signal from your cellphone reveals two of your vital signs: your pulse and
breathing rate. Better still, you don’t even have to answer your phone.

The Bell Labs engineers, led by husband-and-wife team Victor Lubecke and Olga
Boric-Lubecke, noticed that some of the microwaves transmitted by a cellphone’s
antenna bounce back to the phone from the chest, heart and lungs of the person
using it. Because those organs are moving, the frequency of the reflected
radiation is Doppler shifted by a tiny amount. If the lung is expanding, the
radiation bouncing off it is pushed closer together, slightly raising its
frequency. A contracting lung lowers the frequency. The variation is tiny: just
one hertz in a billion.

Bell Labs—owned by Lucent Technologies—now plans to modify the
mobile phone with a circuit that detects the Doppler shift in the reflected
signal picked up by its antenna. The phone then sends this information on to the
base station, where further signal processing extracts the user’s vital signs.
“We’re talking about very low-frequency signals. They’re easy to separate from a
voice,” says Lubecke.

To pick up the reflected signals, the cellphone has to be held steady for a
few seconds, says Lubecke. Which is just what will happen if its owner is
trapped or unconscious. Doctors could also use the Bell Labs technology
routinely to monitor your heart or breathing—just by phoning your
mobile.

Lubecke has been working with James Lin from the University of Illinois in
Chicago to test his ideas. The researchers used a radio with similar frequency
and power to a typical mobile phone to demonstrate the effect in their lab. Now
they are building a prototype detector.

Today’s cellphone networks treat the interference information as unwanted
noise and discard it. For the new system to work, the network will have to be
modified— possibly with a simple software change—to retain and
interpret the signals, says Lubecke.

While the phone must be switched on, you don’t have to answer it for the
system to work: just making it ring generates enough of a signal to allow the
heart and lung data to be piggybacked onto the signal that tells the caller your
phone is ringing.

Lubecke says chest movement is easiest to detect, along with heart rate.
Later, he hopes to be able to tease out information about the strength of
heartbeats, too.

Other experts say the technology faces major challenges. Alan Preece, who
investigates mobile phone health effects at the University of Bristol, says that
the heartbeat signal would be so much weaker than the main signal that it risks
being swamped.

If the Bell Labs discovery can be reliably exploited, it could also help you
get remote diagnoses just by phoning your doctor. So while the jury is still out
on cellphone safety, pending the results of a five-year study by the World
Health Organization, it looks like cellphones may have at least some health
benefits on the horizon.