It's definitely not snake oil, I've used it myself.
I first heard about the DKL Lifeguard from a SEAL who witnessed a live demo, which he said was amazing. It was also mentioned in Tom Clancy's novel "Rainbow 6". I looked it up on the internet, & found the company's website,
www.dklabs.com, amongst a bunch of other websites that were badmouthing them and their technology. I also found the following magazine article, which confirms the company's claims, and explains how the results of the test conducted at Sandia Labs were misinterpreted.
http://www.officer.com/print/Law-Enforcement-Technology/LifeGuard-Tracks-Criminals-Where-They-Hide/1$35704
I was told that another test was conducted at a container port in Europe, in which the device was used to search containers for stowaways, after which the containers were physically searched by port officials. In that test, they searched over 1,500 containers, found stowaways in about 50 of them, and didn't miss a single one, although it did produce a small number of false positives.
I operated it myself shortly after a demo at last year's FPED at Quantico. As a former Marine from the late 60's I immediately knew how valuable a tool it would be for use in combat and security applications.
The company gave me the following point of contact info for one of their representatives, Garry Robb, a former special forces operator with the Phoenix program, and SOG (CCN): He can be reached at:
grobb@epix.net, cell # 610-517-1252.
Note: The image you show is of the original prototype. Here's a photo of the current model, along with the computer used in training operators to use it.