The system operates on rechargeable batteries that take up to 6 hours to recharge but provide 12 hours of operation — if the user operates the system the way DKL advises. Running the system's optional laser significantly shortens battery life, Sidman explains. "The laser is nice because it shows everyone in the search team what direction the detection is in," he says.
Model 25, currently in the prototype phase, is smaller in size than Model 1. This second-generation product will be able to detect people through 1-meter-thick concrete walls within a range of 20 to 50 meters. Designed for the rugged public safety environment, this prototype will also feature reduced battery weight and size, as well as present digital readouts of detection data.
The unit locates and points toward an irregular electric field generated by the human body. Electricity produced by the heart, which makes up 97 percent of this electric field, creates electrical impulses at ultra-low frequencies (less than 30 cycles per second), which travel through barriers that absorb or reflect higher frequency energy.
While the system could be used to detect a variety of electrical frequencies, its designers matched the instrument to a human being's electric field, Sidman says. Because the heart produces the majority of a person's electrical field, the system can find individuals — even when they are immobilized — as long as their heart is beating.
Human beings are not the only living creatures with four-valve hearts, however. If cows, monkeys and other animals also have four-valve hearts, how is it possible to distinguish between them?
DKL equips the device with an SPF filter to differentiate between humans and that of other living creatures or inanimate objects. "We looked at different field presentations and found the human electric field to be unique," Sidman explains. "We then developed a filtering circuit that allows us to match to that specific field." This circuitry ensures the system only reacts in the presence of a human electric field. He describes it as tuning in to a specific station, much like a person does with a radio.
But how accurate is it?
That's a burning question on everyone's minds, admits Sidman, especially since a 1998 test of the product by Sandia National Laboratories reported the system had just six successes in 25 trials.
Sidman explains the negative reports pertain to a prototype that never went into production and no longer exists. He states, "Since we've brought the Model 1 out, 3 1/2 years after the report, we've continued to improve the product, having made five or six hardware changes and improved the software an equal number of times."
He attributes the negative reports to a discrepancy in the definition of a successful detection. Sandia researchers labeled a successful detection as when the device pinpointed a person's location with 100-percent accuracy. "If we were off by a couple of degrees at maximum range, we didn't get any credit," Sidman explains.
But that's not how the device works. The LifeGuard points users in a subject's general direction then becomes more accurate as the operator closes in on the target.
Success also varies by the number of barriers between the device and a subject. "If you are in the open air, it points right at the subject," Sidman explains. But if an officer is 300 to 400 meters away from a person, and there is a lot of barrier (trees, concrete walls, etc.) between them, the device will only point the user in a direction in which to move. The system may be 5 to 6 degrees variant from where the person actually is but as the officer moves closer, and the amount of barrier is reduced, accuracy improves.
"For a search in the woods, we can get within visual distance of where that person is," Sidman says. Once officers close in, they should employ faster procedures, such as search dogs, night vision, or foot pursuits, he adds.
The device can quickly search large spaces to reduce the target search area, which may have a 180-degree arch at the pursuit's onset. "The value is that we can explore that 180-degree arch out to 400 to 500 meters, and if there's someone within that detection range, we can provide a narrower bearing," says Sidman. "Then rather than search the entire 180-degree arch, officers can head out in a 4- to 5-degree area."