Through-the-Wall Surveillance

Market Survey

The NIJ-sponsored Sensors and Surveillance Technology Working Group has completed a market survey of through-the-wall sensor technologies.

Read the report (pdf, 31 pages)

Through-the-wall surveillance (TWS) technology detects motion through interior or exterior building walls. It can penetrate brick, reinforced concrete, concrete block, sheetrock, wood, plaster, fiberglass and common building materials, but not solid metal (e.g., it can "look" through rebar reinforced concrete but not a solid metal wall).  It can be used, for example, to locate and track individuals inside a building during hostage rescue operations.

Some TWS devices must be placed next to the structure; others can operate at a distance from it, enabling building searches from a vehicle or other safe cover.

Refinements in technology and policy have overcome many barriers posed by earlier versions, which were often costly, had to be placed near or directly up against the wall, or were approved for use by the military but not law enforcement.

The NIJ-funded Sensor, Surveillance and Biometric Technologies Center of Excellence has published several reports on TWS technology:

Read the Federal Register Notice for NIJ’s evaluation of through-the-wall sensor devices.

Read an NIJ Journal article, "Through-the-Wall Surveillance: A New Technology for Saving Lives."

Standoff Through-the-Wall Device Approved for Law Enforcement Use

Akela Standoff Through-the-Wall Imaging Radar
Akela Standoff Through-the-Wall Imaging Radar

Akela Standoff Through-the-Wall Imaging Radar
View a larger version that demonstrates how the system works

NIJ supported the development of the first standoff through-the-wall surveillance device approved for law enforcement use. 1 The Akela Standoff Through-the-Wall Imaging Radar; a portable radar system that can, from a distance, map and image the internal structure of a building and locate living personnel inside the structure. It can detect a motion as small as the that of a person breathing. The system can be networked, runs remotely using wired or wireless Ethernet, and provides the controls and display through a regular laptop computer. NIJ is funding further development and testing and evaluation in operational settings.

Read the report Through the Wall Standoff Detection and Tracking of Individuals (pdf, 70 pages)


[note 1] In late 2011, Akela received a waiver from the Federal Communications Commission to produce a system the use of which is "limited to state and local police and firefighters, and … limited to actual emergencies involving threats to safety of life, and necessary training." View the complete text of the waiver on

Date Modified: January 23, 2015