KeyCarbon announced what they call the world's first hardware-based keystroke logger for laptops. There are 3 models that vary based on storage: 16MB, 32MB, and 128MB, which can store 8 million, 16 million, and 64 million keystrokes respectively.
The company cites one caveat for using the product: KeyCarbon says that since the device requires the use of an internal PCI Express slot, which many laptops have available, it can only be used on laptops where the slot isn't already in use.
But there's another caveat that they don't mention. If you have to take apart laptop chassis (as opposed to simply removing user-accessible cover on the bottom) in order to access the PCI Express slot then in all likelihood you void its warranty.
If you're willing to do that then you can buy the device for prices ranging from $199 to $399.