The U.S. military can see you breathing on the other side of that wall. It can even see your heartbeat racing while you crouch behind the door. But if you think running farther away or hiding in a crowd will make you invisible to the Defense Department's sensors, you might be in for a surprise. The Pentagon's geeks are looking to tweak their life-form finder so they can spot your tell-tale heart no matter what you do.

Darpa, the Pentagon's mad-science shop, announced last week that it's looking to improve on technologies that sniff out biometric signatures like heartbeats from behind walls. Dubbed "Biometrics-at-a-distance," the program seeks to build sensors that can remotely identify humans from farther away and tell them apart in a crowd.

Seeing or "sensing" human life through walls can be a pretty helpful trick. For troops that have to clear houses in search of terrorists or insurgents, it's always nice to know what's on the other side of that door. Picking up "life-form readings" may sound like science fiction straight out of Star Trek, but the Defense Department has been able to do it for years now.

In 2006, Darpa developed Radar Scope,which used radar waves to sense through walls and detect the movements associated with respiration. A year later, the Army invested in LifeReader, a system using Doppler radar to find heartbeats. More recently, the military's been using devices like the AN/PPS-26 STTW ("Sense Through the Wall") and TiaLinx's Eagle scanner, which can sense the presence of humans and animals through walls.

Handy though these gadgets may be, Darpa wants to one-up them with some new and better capabilities.

First off, Darpa wants its biometric device to be able to work from farther away. Right now, it says the accuracy of most systems taps out at around eight meters. And while some see-through devices can see through up to eight inches of concrete, they don't do as well in locations with more or thicker walls. So Darpa's looking for the next system to push that range past 10 meters, particularly in cluttered urban areas.

Finding humans hiding in a particular room is nice, but being able to tell them apart is even better. Like your fingerprints, irises and even your veins, your heartbeat can be a unique biometric calling card to distinguish you in a crowd. Darpa's hoping its sensor can capitalize on this by using electrocardiography – the analysis of the heart's electrical activity – to identify and track up to 10 different individuals.

But don't be too scared of Darpa's heart hunter. There are plenty of non-terrifying applications that the Pentagon's geek shop envisions for the device. For instance, being able to sniff out life signs at longer distances and behind thick concrete slabs could be very useful in disaster scenarios. In the aftermath of an earthquake, rescue workers could use Darpa's longer-range biometric sensors to find survivors trapped under rubble.

Photo: bludgeoner86/Flickr