Enable, Disable Toggle Button
Windows Precision Touchpad devices (or legacy touchpad devices that were configured for enable/disable control in Windows 8.1), can have their enable/disable state toggled via a hardware button, or a keyboard combination.
For convertible devices that implement integrated touchpads on keyboards that can be folded back, a device driver that typically disables keyboard or button features can also disable the precision touchpad. To disable the precision touchpad, the device driver should first query the following registry key:
If this value is non-zero, the driver can issue a hotkey combination [CTRL + WIN + F24] to toggle the precision touchpad OFF. If the keyboard is no longer folded back, and the value of the registry key is zero, then the driver can toggle it back ON.
Note This registry key is read only, and is not to be modified directly.
So in short, the state of the touchpad will be toggled when the CTRL + WIN + F24 keyboard combination is reported to the host.