When Hansel and Gretel ventured into the forest, they left a trail of breadcrumbs to find their way home. In today’s world, cellular phones, Global Positioning System (GPS), WiFi, and Bluetooth are the digital signals that connect us to friends, family, and colleagues while helping us find our location and map our routes.

Yet, despite the ubiquity of such devices, with few exceptions, today’s firefighters still rely on 20th-century radios, whose outdated analog signals have trouble penetrating debris and concrete. When a firefighter heroically plunges into a smoke-filled building, tunnel, or forest, a UHF radio or, for that matter, even a GPS satellite signal won’t follow. The firefighter vanishes from the map.

For a first responder, radio silence can be lethal.

That’s why the Department of Homeland Security’s (DHS’s) Science and Technology Directorate (ST) is combining two previously developed heatproof and waterproof wireless monitors with a newly developed technology. Working together, the three technologies could lead to a life-saving solution.

One device, the Geospatial Location Accountability and Navigation System for Emergency Responders (GLANSER), crams a microwave radio, a lightweight battery, and a suite of navigation devices into a tracking device the size of a paperback book. Back at the fire truck, GLANSER’s signals are received and transmitted by a small, USB-powered base station plugged into a laptop. As firefighters move from room to room and floor to floor, the laptop display animates their every step.

A second device, the Physiological Health Assessment System for Emergency Responders (PHASER), can monitor a firefighter’s body temperature, blood pressure, and pulse, relaying these vitals back to the base station. If a firefighter falls or faints, fellow firefighters can race in, quickly find him, and bring him to safety, guided by GLANSER.

Like the first cordless phones, GLANSER and PHASER transmit at 900 MHz-a frequency that can penetrate walls, given a decent-sized transmitter. But because of their portable size, the transmitters are extremely modest. Their signals could be stopped by a wall, or-in a wildfire-by a wall of trees, unless relayed by routers. That presents an infernal challenge.

What’s needed is a self-powered router that can take the heat.

ST is developing a tiny throwaway router, measuring one inch square by – inch thick, that’s waterproof and heat-resistant up to 500- F. The Wireless Intelligent Sensor Platform for Emergency Responders, or WISPER, contains a two-way digital radio, antenna, and 3-volt lithium cell.

Here’s how it works: Each firefighter enters a burning building with five routers loaded into a belt-mounted waterproof canister. If a firefighter steps behind concrete or beyond radio range, the base station orders his canister to drop a “breadcrumb.” The dropped routers arrange themselves into a network. If a router accidentally gets kicked down a stairwell or firehosed under a couch, the WISPER network will automatically reconfigure.

To an embattled firefighter, a handful of these smart “breadcrumbs” could spell the difference between life and death.