I am interested in cost effective and creative ideas for detecting physical attacks against computer systems. This includes, but is not limited to Tamper Evident security measures.
Consider the following attack scenario: An attacker would like to obtain data from a harddrive. The target machine is setup with Full Disk Encryption, a bios password is set and the boot priority states that the encrypted drive is the first device to be booted.
The passphrase must be typed in order decrypt the drive and boot the machine. A Hardware Keylogger could be installed to obtain this value. Some full disk encryption implementations can be defeated with Bus Sniffing, however in order to carry out this attack the computer case must be opened. In either attack, after a period of time the attacker can return and collect the harddrive and intercepted passphrase.
How can you detect if your computer case has been opened? How can you thwart the use of a hardware keylogger?
Also here is a great talk on Bypassing Tamper Evident Devices.
Edit: The state of modern physical security is incredibly poor. Literally every door lock available at my local Walmart can be picked in seconds. Most homes in the US are still using pin tumbler locks that originally invented by the Egyptians thousands of years ago.