According to Toshiba, the new wipe technology on their self-encrypting hard drives will destroy any data in them when you remove the device or power it off completely. Sounds a bit nuts, but it makes sense.

Instead of over-writing the data—which takes hours—or using a physical method—that requires time and effort—the new drives will automatically invalidate the data in just a few seconds by erasing its HDD security key when the power is completely off. This means that any confidential documents stored in the hard drive—like an office printer—will be safe in case someone extracts the HD or the device is stolen and disconnected from the power outlet.

I'd hate to lose power to my house