Even though firefighting is one of the most dangerous jobs in the world, firefighters still communicate using analog radio signals, that can be blocked by concrete walls. This means that, upon venturing into a burning building, a firefighter might have no way of letting their commander know their present location - a situation that could prove deadly, if they ended up trapped or injured. In order to address the situation, the U.S. Department of Homeland Security's Science and Technology Directorate has created a new three-part system that lets fire crews keep track of the location and well-being of every member of their team, all the time.

The first part of the system is a paperback book-sized tracking device known as the Geospatial Location Accountability and Navigation System for Emergency Responders (GLANSER). Using its microwave radio, lightweight battery and various navigation devices, GLANSER sends and receives signals to and from a small base station module, which is plugged into a laptop located back at the fire truck. On the laptop's screen, a graphic display constantly indicates the firefighter's location within the building, no matter where they go.

Besides GLANSER, firefighters would also wear a Physiological Health Assessment System for Emergency Responders (PHASER). The PHASER monitors body temperature, blood pressure, and pulse, and relays these parameters back to the base station. If the firefighter were to pass out, the PHASER output would indicate as much. Using GLANSER as a guide, other firefighters could then locate and rescue them.

It sounds good so far, although in order to remain portable, the transmitters for the two devices are quite small - potentially too small, in fact, to generate a signal that can penetrate walls. That's where the Wireless Intelligent Sensor Platform for Emergency Responders (WISPER) routers come in.

Each disposable WISPER unit measures one square inch by half an inch thick (6.45 sq.cm. x 1.27 cm.), is waterproof, and heat resistant up to 500F (260C). It contains a two-way digital radio, antenna, and 3-volt lithium battery. Every firefighter would wear a belt-mounted waterproof canister, that contained five of the units.

As soon they stepped behind a concrete wall or otherwise went out of GLANSER contact, the base station would instruct the canister to automatically drop a WISPER router. It would continue dropping them periodically, as long as the firefighter was out of contact. The dropped units would form a network, each relaying the GLANSER and PHASER signals, until they reached back to the base station. Even if one of the units got kicked or hosed out of place, the network would be able to reconfigure itself.

In order to get the most life out of each unit's tiny battery, WISPER utilizes the low-power Zigbee communications protocol. At no more than 100 kilobits per second, it's over 99 percent slower than Wi-Fi. That may be slow, but still fast enough to transmit the basic data required.

While GLANSER and PHASER are already existing products, Homeland Security is now trying to find a company interested in manufacturing the WISPER routers. Once production is under way, the entire system will be tested for performance and consistency.