Deadman is an anti-forensic linux kernel module deadman-switch will shut down the system once the load-time specified USB device gets removed.
Inspired by silk-guardian, but much simpler in scope.
Build & Use
make sudo insmod deadman.ko usb=0xVENDPROD
(VEND is the 2-byte hexadecimal code for idVendor and PROD for idProduct)
Before building, the usb parameter can also be set to some default instead of 0.
When the drives your machine are fully (or partially) encrypted, they are still vulnerable when in-use, unencrypted. Requiring the specified USB device to remain connected is an added security feature; once the system is down, all encrypted data is only accessible by decrypting it first.
When a USB device is strapped to ones wrist, it will be harder for third parties to prevent the device to be removed when attacked.
Silk-guardian has broader uses, it can also shred certain files (in case no encryption is in use), it can respond to unknown USB devices (such as a "mouse jiggler" as used by law enforcement to keep the system from sleeping, or a USB drive that someone is wanting to copy files to).