I would like to set up my computer's full disk encryption to unlock with a key file (preferably one that uses the SD card interface, but I'm not particularly picky) because it's annoying to enter in long passwords every time I boot my computer, but I don't like the idea of anyone with the "key" being able to open my computer.
My preferred compromise would be a memory card / stick that has a small key file on it, with a random 100-200 character password that I could easily and securely wipe by flipping a switch. This way, I could keep the password backed up for manual entry elsewhere, and use the key for convenience during day-to-day life, if I feel like I'm going to be in a situation where someone might demand the key of me (or if I'm otherwise going to be separated from the key), I could easily and surreptitiously wipe its memory. Ideally, it would err on the side of failing (e.g. fail closed rather than open), since it's not the only place the information is stored.
For hopefully obvious reasons, it would need to be something that I can wipe without putting it in a computer, so something like a powered device that stores the key in volatile memory would work well, I imagine, or something that has a small battery that can be used to erase itself.
Does anyone know if such a device exists, and if so, what are they called?