Your monitor is a transmitter, and it always has been
2026-02-19 · EA5IYR
Every wire carrying a fast-changing electrical signal radiates some of it. This is not a defect. It is what an antenna is, and there is no way to make a wire that does not do it at all — only ways to make it do less.
An HDMI cable carries a signal that changes tens of millions of times per second. It radiates. And what it radiates is, in a recoverable sense, the picture. The old name
The technique is called Van Eck phreaking, after Wim van Eck, who in 1985 published a demonstration that the contents of a CRT monitor could be reconstructed at a distance with modest equipment.
The military had known for decades. The relevant US standard is TEMPEST, and the details were classified long enough that van Eck's paper was, for a lot of people, the first public confirmation that the problem was real. Why digital did not fix it
There was a reasonable expectation that flat panels and digital cables would end it. They did not.
HDMI sends data at a clock rate, and the harmonics of that clock land squarely in bands a cheap software radio can hear. The relationship between what is on the screen and what comes off the cable is more complicated than it was with a CRT — which for a while meant the recovered image was a smeared mess.
Recent published work applies machine learning to that mess. Given a model trained on what HDMI emissions look like, the reconstruction becomes markedly more readable. The hardware required is an RTL-SDR dongle, which costs about as much as a takeaway. What this is and is not
It is not a way into your computer. There is no malware, no network access, nothing installed, and nothing to find afterwards. It is passive listening to something the machine is doing anyway.
It is also not effortless. You need to be reasonably close, you need to identify the right frequency, and interference is your friend rather than the attacker's — a normal office full of equipment is a difficult environment.
But the threat model matters. If you are handling something where a determined party would park a van outside, this is a real consideration, and it is why secure facilities have shielded rooms, filtered power and specified cabling. That is not paranoia; it is a building code. The pleasing part
For everyone else it is mostly a demonstration of something true and slightly unsettling: your equipment is on the air whether or not you meant it to be. Point a wideband receiver at your own desk sometime and see what is coming off it.
You will find that a room you thought was quiet is nothing of the sort.
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Sources: Wikipedia — Van Eck phreaking, arXiv — Deep-TEMPEST: eavesdropping on HDMI from unintended emanations, RTL-SDR.com — Deep-Tempest, Kaspersky — Deep-TEMPEST side channel.