You probably know that your activities on a computer or mobile device that uses Wi-Fi might be monitorable by Internet providers, sites you visit, and perhaps hackers and the government. But, did you know that by analyzing Wi-Fi signals people can also spy on you physically, seeing when and how you move, and monitoring what you say or write?


This month, a group of researchers at Northwestern Polytechnical University in China shared information online about a system that they claim can, with sometimes greater than 90% accuracy, identify people based on how their bodies affect Wi-Fi signals. This follows a similar study by Australian and British researchers, other research done in Asia, and work done at MIT that found that by analyzing Wi-Fi signals one can detect if someone in a room nearby is waving his or her hand.

How is this possible?

Wi-Fi, of course, uses radio frequency transmissions. Anytime that you are in an environment in which there is Wi-Fi, it is not just your electronic devices that the Wi-Fi affects; you are absorbing some radio waves and causing others to bounce in various directions off your body. (There is ongoing research into whether this creates health risks - let us hope that it does not.)

By analyzing how a Wi-Fi signal is altered when a particular human moves through it, therefore, researchers can determine the person's shape, position, and movement. Armed with enough knowledge - such as what a person looks like and/or how he or she walks - someone with an analysis system could determine the identity of a particular person.

But the privacy risks are even greater. Careful analysis of the impact on Wi-Fi signals of a human moving also allow a party to determine what a person is saying by reading his or her lips, or read what a person is writing with a pen (after all, both mouth and hand movement impact Wi-Fi signals).

The Wi-Fi access point or router does not even need to be in the same room as the person being monitored. As long as there is sufficient signal to analyze the impact of motion, all sorts of spying is possible. To make matters worse, the person doing the monitoring could be the one supplying the Wi-Fi signal.

The Chinese researchers claim that in their tests, in which they pre-loaded information about various people's body shapes, their monitoring system could identity which of two people walked across its line of sight with 95% accuracy. When given six possible choices, the system was right 89% of the time.

Of course, such technology could also be used for good - for example, to detect home invasions in the middle of the night, or if an elderly person falls and cannot get up. Wi-Fi analysis could ultimately be used to trigger alarms in cases of other forms of medical emergencies; the aforementioned MIT researchers claim that by analyzing changes in Wi-Fi signals one can remotely monitor a person's breathing and heart rates with 99 percent accuracy.

As far as we know, all of the aforementioned Wi-Fi scanning and analysis is still in the research phase. Governments, of course, might have already developed such technologies, but, if they have, they have kept them a secret. In any case, keep in mind that wherever there is Wi-Fi or any other radio signals, it is possible that someone could use them to "see" things that seem invisible. Top secret conversations, for that reason, should take place in environments shielded from radio transmission leaks. In fact, for such reasons, and to prevent possible leaks of data via similar analysis of electromagnetic fields, the government implements secure, shielded areas in various secure facilities.