Watched over wirelessly (Image: Alex Bramwell/Getty)

It’s not easy sleeping with tubes up your nose, but when doctors want to monitor a person’s breathing they have few other choices. A new wireless system promises to do away with intrusive medical technology – but instead it might end up being used as a surveillance tool to track people’s movements and activities behind closed doors.

While testing some new equipment, Neal Patwari of the University of Utah in Salt Lake City and colleagues noticed variations in wireless signal strength triggered by a person’s breathing, but only at certain locations around the room. So they set up an experiment to test whether a wireless network could reliably measure breathing rate.

In the test, Patwari lay in a hospital bed surrounded by 20 inexpensive, off-the-shelf wireless units. These were arrayed so that they sent 2.4 gigahertz radio waves across the bed – the same frequency as Wi-Fi – but with one-thousandth the power of a laptop’s wireless card. The units measured the signal strength four times a second – fast enough to measure fluctuations caused by individual breaths.


After collecting 30 seconds of data, the network was able to accurately estimate a person’s breathing rate to within 0.4 breaths per minute.

Patwari concludes that the wireless signals bent around his chest as it rose with each inhalation, causing them to travel a longer distance and decrease slightly in power.

Unmasking

The technology could allow people to rest more comfortably during sleep studies, Patwari says, without being connected to machines by wires and tubes. He contends that the system could be used to augment current medical tests for lung capacity, too.

But current medical breathing monitoring methods are more than adequate, says Salvatore Morgera at the University of South Florida in Tampa. These methods also measure the amount of carbon dioxide in exhaled gases, collected in a mask or a tiny tube in each nostril, whereas wireless monitoring would just increase the clutter of radio waves in a modern hospital.

If it doesn’t find a use in medicine, the device may still interest snoopers. In a previous study, Patwari and a colleague showed that because radio signals at Wi-Fi frequencies can penetrate walls, a wireless network set up outside a home could track people as they move from room to room. With this new level of precision, a system tailored for surveillance could spy on people as they move around a hotel room, for example, or even discern whether they are resting on a couch or in bed.

Journal reference: arxiv.org/1109.3898