Look into PAM configuration. In particular I think you'd probably want some combination of pam_faillock and pam_exec. pam_exec can be used to call some arbitrary script to wipe your disks and possibly be extra evil and call flashrom to even wipe the firmware beforehand.
Actually wiping the disk would take way too long. Assuming that you're running Linux and that all connected drives are fully encrypted: overwrite all keyfiles in a secure manner (ie flushing all caches and etc), write random garbage to the entirety of RAM, and trigger the equivalent of `halt -ff` (note the double --force).
Bonus points for additionally finding a way to trigger the "secure erase" firmware feature of all attached devices as part of the above sequence. That's likely to prove a bit tricky though since that feature is generally locked out (for obvious reasons) once you leave the bootloader.
By "wipe your disks" I meant issue a secure erase assuming you have a SSD like Intel's where it would overwrite an encryption key and be done in short order.
The contents of RAM in this scenario shouldn't be particularly vulnerable. If they're trying random passwords on the actual machine without any attempt to preserve the disks beforehand there's zero chance they're about to take the machine apart and extract what's left in RAM before it's gone.
>Potentially of interest: `__noreturn machine_real_restart` in reboot.c
Just write "b" to /proc/sysrq-trigger, it'll immediately trigger an ungraceful reboot without trying to unmount filesystems or flush the cache.
