{
  "id": 19295187,
  "title": "Your TV can see through walls",
  "url": "https://urgent.news/2026/11/10/your-tv-can-see-through-walls",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-11-10T05:24:45.000Z",
  "source": {
    "name": "Hacker News",
    "slug": "hacker-news",
    "url": "https://maurycyz.com/projects/fading/"
  },
  "original_language": "en",
  "account": "A simple radio receiver, such as one used to tune into local TV stations, can detect motion and estimate speed. This is demonstrated by using an Ettus USRP B200 to record signals from a digital TV signal, or ATSC digital TV signal. Walking between the receiver and the TV station causes a slight disturbance to the signal. However, when the antenna is moved a few centimeters, selective fading occurs, where the direct signal is canceled out by a strong reflection. The phase of the reflection depends on frequency, causing the effect to be not uniform over the whole signal.\n\nThis sensitivity to nearby movement was tested by the author getting up from their chair and walking around a neighboring room. The gaps between the stripes in the signal spectrogram happen when the reflection perfectly cancels out the residual signal, which occurs each time the path length changes by one wavelength. By measuring the gap between each stripe, the author calculated the speed of their walking motion. The gap between each stripe was around 70 pixels, and the waterfall had an update rate of 150 Hz.\n\nThe author found that 70 pixels multiplied by 1 second per 150 pixels equaled 0.47 seconds, which was equal to a speed of 2.1 Hz. Using the speed of light (490 MHz) and the calculated speed of 2.1 Hz, the author determined their walking speed to be 1.3 m/s, or 4.6 km/h. The motion detection and speed estimation were found to work not just for TV signals, but any wideband radio signal like WiFi or LTE, albeit with a more challenging spectrogram to work with.",
  "summary": null,
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}