Neal Patwari of the University of Utah discovered that breathing affects Wi-Fi signal strength. Chest expansion during a breath bends the wireless signals and they lose some power. This slight drop can be measured and used to calculate your breathing rate.
Measuring someone's breathing rate is helpful, but the use of this technology as a spy tool is where things get interesting. In an earlier study, Patwari discovered that any movement can affect wireless signal strength and these changes in strength can be use to track your location within a room. He also discovered that these small changes can measured even when the Wi-Fi signal passes through a wall and travels into another room.
So a snoop who wanted to spy on you could theoretically setup a wireless network outside your house, measure signal strength changes and track your movement inside your house. It's supposedly sensitive enough to detect whether you are standing up, sitting or lying down. [Cornell University via New Scientist]
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