When dealing with sensitive data on your computer or server, nefarious people are always trying to seize and take your computer. Computer forensics is getting more and more sophisticated, and now people are able to take your computer without powering it down, using a variety of products, one called
HotPlug (see link #1). Very cool. This type of product enables the taker to potentially keep encrypted drives decrypted, passwords typed in, and access to a lot more data than if they shut the PC down. Plus any crypto keys would still be stored in memory, and the taker could take the computer home, freeze the memory, dump the contents of the memory, and then whamo, they've got your crypto keys. Oops.
How to get around this? A cryptographic signal, sent between a signal generator somewhere in the house, over the AC in the house, similar to how X10 sends signals over AC, to a special PSU (power supply) in the computer.
The firmware in the PSU and the firmware in the signal generator are set using the same crypto key (or a Public/Private key), so that the PSU and signal generator know what to send and receive. The signal changes with time, as with one-time passwords, and using A-GPS (which can work indoors) to generate the signal, prevents moving of the signal generator to another location.
If the signal is incorrect at any time, the PSU can start a user-defined process -- disk wiping, shutting down disk decryption running in memory to prevent physical freezing of memory to retain the crypto keys used for decryption (see link #2), some sort of physical destruction of platters or SSD, etc. The PSU would be somehow connected to the system and would be able to take action without changing the screen output (in theory), without letting on that something is occurring in the server that might prevent forensic analysis or data theft.
Sure, this would suck if your wife unplugged your signal generator accidentally, or a power surge took out the signal generator, but not your PC, or the power went out and the signal didn't come through to your PC. But better safe than sorry.
Likely users would include corporations who store sensitive data, and physical theft of sensitive data could cost them millions or billions of dollars; lawyers that keep highly confidential data in central servers; the government, who we all know are keeping big files on all of us. :-) hehe
With quantum computing gaining traction and feasibility, that too could be used instead of cryptographically generated signals.