> full of digital signals sent in unpredictable My opinion is digital signals are the very antithesis of "unpredictable", it's always an exact replication. Of

> full of digital signals sent in unpredictable My opinion is digital signals are the very antithesis of "unpredictable", it's always an exact replication. Of course it may look like garbage (and sometimes even intentionally scrambled to garbage for electrical reasons) to the naked eyes without interpretation, but many things are possible after signal processing. > manufacturer-specific ways First, there are industrial standards on display interfaces, for example, there are well-defined ways to send a video signal, such as HDMI to the monitor, and LVDS (a specific version of LVDS) from the monitor to the LCD panel. The majority of LCD screens use these standard. Second, even when there's no standard, similar architectures are used across different systems, for example, most LCD drivers on the market are similar to each other. Discovering a way of doing it on a new system is not exactly a surprise. > and certainly not sequentially enough to leak as recognizable audio. All you need to do is doing something periodically. Even if the activity you're doing is at low frequency, often it influences some high frequency signals so that a signal can be modulated. As a thought experiment, if you write something to RAM with all 1s and all 0s once every few seconds, it's very reasonable to assume it creates a detectable burst of radiation on the RF spectrum even if the bus itself runs at a higher frequency. In practice it's more subtle and specific from system to system but there's often a way. For example, it's possible to modulate a computer's memory bus to emit AM audio by accessing the memory in a specific pattern using a few lines of assembly code, whether on a PDP-11 or a MacBook, it's possible to modulate the mechanical vibration of inductor coils on the CPU power circuitry to emit audible music on a Thinkpad by rapidly changing the CPU power state, etc. There are endless number of ingenious ways of doing it, if you have control over a process.