Is Your Router Snooping On You?

Over the past year, we have seen some incredible (and slightly frightening) developments in repurposing wireless signals for sensing applications. WhoFi, for instance, can uniquely identify individuals, even through walls, by using the Wi-Fi signals that already surround us almost everywhere these days. Now — for better or worse — a team led by researchers at the University of Texas at Arlington has improved the sensing capabilities of these types of systems.

Their new system, called LoFiSen, goes beyond conventional Wi-Fi sensing by merging two unrelated wireless technologies: LoRa and Wi-Fi. While Wi-Fi is nearly ubiquitous in homes, offices, and public spaces, it suffers from a surprisingly short usable sensing range — typically no more than 3–8 meters. LoRa, on the other hand, can cover long distances but isn’t widely deployed indoors. Instead of trying to fix the shortcomings of either system independently, the researchers took an unconventional approach: why not make them work together?

With LoFiSen, a LoRa transmitter and a standard Wi-Fi device operate as a sensing pair, effectively transforming everyday networking hardware into a long-range motion and respiration monitoring platform. In experiments, the team demonstrated that this hybrid method extended Wi-Fi sensing range from 8 meters to an impressive 41 meters for respiration tracking, and expanded walking detection from 16 meters to nearly 74 meters. Even more impressive — and perhaps more unsettling — the system can perform through-wall passive respiration monitoring, something that has long been considered out of reach for pure Wi-Fi sensing.

LoFiSen’s key innovation involves enabling Wi-Fi routers to “listen” to LoRa signals without requiring any hardware modification. This might sound impossible, as the two technologies use completely different protocols, but Wi-Fi devices continuously monitor channel energy through a process known as carrier sensing. The researchers cleverly exploited this mechanism to extract LoRa signal strength (RSSI) indirectly. There was only one problem — LoRa chirps hold their useful information in frequency variation, not signal amplitude, which means the RSSI alone conveys almost nothing.

But the team overcame this problem by using two LoRa chirps simultaneously — one increasing in frequency (upchirp) and one decreasing (downchirp). While each chirp independently has constant amplitude, their superposition produces amplitude fluctuations that Wi-Fi hardware can record. These fluctuations reveal the frequency characteristics needed for sensing. Because commodity firmware samples signal energy at a relatively slow rate, the resulting data is heavily aliased and distorted. But the researchers designed mathematical methods to reverse that distortion and recover the underlying motion information.

This technology could open the door to hospital patients being tracked without wearables, or homes being equipped with passive elder-care monitoring that never requires anyone to strap on sensors. At the same time, the ability to detect breathing through walls raises familiar debates over privacy, consent, and surveillance creep. Like so many new technologies, LoFiSen’s future depends not just on what is possible, but on how we choose to use it.