The ability to sense the presence of individuals through common building materials can be useful during rescue operations, law enforcement operations, and other tactical scenarios. Firefighters could use the devices to locate trapped survivors. TTWS can display a variety of information, from the simple "movement detected" to a two-dimensional graphical representation of detected movement in relation to the sensor. Devices may also provide a graphical representation of repetitive movement, as would be expected in the detection of breathing. Some data interpretation may require training on the instrument for optimal use. A summary is provided of the commercially available Federal Communication Commission certified TTWS systems suitable for law enforcement or emergency response application. Information provided includes the product name and manufacturer, unit cost, training required, operating range, field of view, weight, battery life, and frequency. The section on "Best Practices and Lessons Learned" offers advice as follows: Practice with the device and learn how to use it; think of TTWS as a tool, but not a substitute for tactical training; take multiple measurements at different places to establish more reliable situational awareness; and metal can block radar signals or confuse results. References and a section on frequently asked questions