Radio Signals Can Turn TVs Into Motion Detectors
Research demonstrates how ATSC digital TV signals can be used to track movement and speed in nearby rooms.
A project detailed on Hacker News reveals that standard radio signals, such as those from local TV stations, can be leveraged to detect human movement through walls, as first reported on Hacker News.
Using an Ettus USRP B200 to record ATSC digital TV signals, the researcher demonstrated a phenomenon known as selective fading. This occurs when a direct signal is canceled out by a strong reflection. Because the phase of these reflections changes based on frequency, the signal becomes hypersensitive to nearby movement.
According to the Hacker News report, this sensitivity allows a simple radio receiver to detect when a person stands up or walks in a neighboring room. By analyzing the gaps in the signal's waterfall—which update at a rate of 150 Hz—the researcher was able to estimate walking speed. In one specific test, the researcher calculated a walking speed of 1.3 meters per second (4.6 km/h) by measuring the distance between signal stripes.
While the demonstration focused on TV signals, the report notes that any wideband radio signal, including LTE or WiFi, could potentially be used to extract similar motion data, although those signals produce a more complex data output.