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Wi-Fi sensing lets you monitor motion in your home – without cameras or motion sensors. We weigh the pros and cons of this increasingly popular technology.
 
Wi-Fi can be used to track people’s (and pets’) movements in the home — from the tiniest gestures, such as hand waves. This application of Wi-Fi is nothing new in theory, but only recently has it been put on a commercial footing. The technology is now being offered by home internet providers and equipment vendors. It may even be incorporated in the new Wi-Fi standard, so it’s important to understand the associated pros and cons. Let’s see how the technology works, whether it poses any privacy risks, and how to disable it if necessary.

How Wi-Fi sensing works

Wi-Fi sensing came about as a side effect of the quest to speed up Wi-Fi. Modern routers have the ability to focus the signal on devices they exchange data with, making the connection faster and more reliable. Known as Wi-Fi beamforming, this technique involves the router measuring the radio signal with sufficient accuracy to determine not only its strength but also its propagation in space. Based on these parameters, the router beams the signal in the direction of the device, and uses channel state information (CSI) to continuously monitor and adjust the communication link.

During the data exchange, if interference of some kind appears between the device and the router, say, a person or a dog passes by, the shape of the radio signal will change slightly. The router is sensitive enough to detect this, effectively making it a motion sensor.

Then there’s just the small matter of developing mathematical algorithms that can detect movement in the home based on changes in CSI, and implementing them in the router firmware. And to receive analytics and signals about motion events, the router communicates with a mobile app on the user’s smartphone, for which a proprietary cloud service is used. Smart doorbells or video baby monitors work in exactly the same way.

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