For future refence:
In light of answers and critique, my question should have been:
1. How does one make sure a physical attacker with access to a powered, but locked FDE PC fails his/hers attempt to clone the harddrives by somehow trigging a computer shutdown. But, in light of answers, it became clearer that "tripwire" shutdown is not essential in the goal of defending FDE.
I am looking and praying for a software that will shutdown computer if it is not approached correctly. An ideal functionality example: the computer is locked, but if the mouse gets moved or any key excepct e.g. "s" is pressed the computer will force shutdown.
edit: there is clearly a market for this, no? An unmonitered, powered computer obviously means full-disk encryption is eliminated. The mightiest of defenses laid on its knees, with nothing but a windows password left to savagely hack.
edit2: (lack the rep to comment) shutdown if X failed pass attempts is good, but if the attacker goes straight for reading the harddrives with external hardware he/she will only move the mouse to check the state of the PC. To clarify, I'm not sure, but I assume there are tools to clone hardrives with a PHYSICAL presence from a powered computer, despite it being locked, if this is impossible correct me.
Edit: 3 I think a rephrase is in order. How would I protect myself from a physical attacker with harddrive cloning tools?
Jeff, how can a clone be a clone with encrypted PC being on/off (=decrypted/encrypted)? Or have I misunderstood how cloning with FDE works? I assume that to successfully clone a FDE PC it must be powered and decrypted, if it is off/encrypted obviously the clone data will be garbled?
Karalga, TPM was a good heads up, I'd never heard of it before, but it makes a lot of sense. As for protection against Van Eck phreaks and such I take my tin-foil hat off to whoever goes that far.