"…how to place a hook in the WM device in order to listen for all hardware button presses. As a matter of fact, Windows CE does support a keyboard hook through the SetWindowsHookEx API. This API requires the usage of the native callback, which was not possible in the first version of the CF. The current version of .NetCF empowered us with this very useful capability. So what are hooks? Put shortly, a hook is a function that you can create as a part of your application in order to monitor on the messages inside the operating system. Hooks were provided by Microsoft primarily to help developers with the debugging their applications. The incorrect usage of them very easily could bring the system down."

Alex Yakhnin - Keyboard hook in the CF v2