Through-the-wall sensor technology a potential life-saver

This tool would increase situational awareness in tactical and rescue situations for police and other first responders

By Becky Lewis
Tech Beat Magazine

All looks quiet at the suburban residence, no lights in the windows, no car in the driveway. The neighbors haven’t seen anyone come or go for several days.

Unknown to the officers outside with the warrants, the house isn’t empty. The person they’re looking for is inside, hiding in the dark, weapon at the ready, but the officers can’t see through the wall to know he’s there.

No equipment exists that would give those officers the capability to actually see through the walls, but a developing technology known as through-the-wall sensor (TTWS) uses radar to detect even slight motions through building walls, thus providing public safety professionals with increased situational awareness in tactical and rescue situations. The Sensor, Surveillance, and Biometric Technologies Center of Excellence (SSBT CoE) has implemented a number of projects to test and evaluate this technology — some of them complete and others nearly so — to help criminal justice agencies make informed decisions about its purchase and use.

“TTWS certainly can provide useful information, and there are no comparable approaches to getting this type of information,” says Lars Ericson, SSBT CoE director. “It’s a unique capability, but it is not foolproof. Officers can use the readings to help them make decisions, but they still need to rely on their training and experience to help them decide how to proceed. TTWS is not the end-all and be-all. It’s just another tool to help law enforcement in specific situations.”

SSBT CoE’s multipronged approach to studying TTWS technology stemmed from a high-priority need identified several years previously by the Office of Justice Programs’ National Institute of Justice (NIJ) Sensors and Surveillance Technology Working Group (TWG). The first result of that approach, a market survey of available technologies titled Through-the-Wall Sensors for Law Enforcement: Market Survey, became available electronically via JUSTNET, the website of the National Law Enforcement and Corrections Technology Center (NLECTC) System, in October 2012. SSBT CoE plans to produce several other publications on the topic, including an evaluation report and a best practices/lessons learned guide.

“No one had really published a reference for law enforcement agencies that are interested in buying a TTWS device,” Ericson says about Through-the-Wall Sensors for Law Enforcement: Market Survey. “At this point in time, only a handful of viable commercial systems are available due to their specialized nature. In addition, the survey looked at current government R&D efforts, which also makes it beneficial to federal agencies and vendors that are in the process of developing the technology.”

Although the market survey became the first task to reach completion, the major component of the effort has been evaluation of a prototype device developed by AKELA, Inc., with NIJ funding. The first TTWS devices on the market primarily targeted military use; the TWG identified a need for affordable devices that also offer increased portability, leading to the NIJ-funded project.

Testing and Planning
AKELA delivered the prototype AKELA Standoff Through-Wall Imaging Radar (ASTIR) in mid-2012. SSBT CoE developed a plan to evaluate it that uses capabilities of the three devices that already have received Federal Communications Commission (FCC) certification as a benchmark. (Although vendors are not explicitly prohibited from selling noncertified devices, the FCC restricts the operation of TTWS to only certified devices and only by public safety and law enforcement agencies.)

Evaluation planning began in spring 2012, and approximately a year later, SSBT CoE has nearly completed the task of testing the devices’ key variables in a number of extensive scenarios. Throughout the process, the CoE has worked closely with the U.S. Department of Homeland Security (DHS) SAVER program, which has been performing research on a parallel track that lags the SSBT CoE project by approximately six months.

“Our research doesn’t duplicate theirs, it complements it,” Ericson says. “Ours takes a more scientific/engineering point of view, and theirs is practitioner oriented. They’ve benefited from the research we put into the market survey and have leveraged our engineers as subject-matter experts to participate in a focus group, where they have demonstrated the technology for practitioners. It’s been a good sharing of resources,” Ericson says.

In addition to continuing to assist the DHS effort, staff members are wrapping up testing and data analysis and preparing a report for NIJ review. Publication on JUSTNET is anticipated for late 2013.

SSBT CoE is also preparing a report on TTWS best practices and lessons learned to aid agencies in the use of this technology. Any departments with prior TTWS operational experience are encouraged to contact the center at or (304) 368-4228 to share their experiences.

For more information on the programs of the Sensor, Surveillance, and Biometric Technologies Center of Excellence, contact NIJ Program Manager Mark Greene at (202) 307-3384 or

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