Okay, I propose a shortest-key-logger challenge. As explained by the gentleman at "Are key-logger questions allowed?", strict rules have to be imposed in order to make this challenge valid for PPCG.
The key-logger has to run on Windows, Linux or Mac OSX (any programming language is welcome).
Upon execution, it has to show the message: "I'm gonna log you" (either in a console or using GUI).
The keys that are relevant for logging in this challenge are letters (case is not important) and numbers, all others such as symbols, control keys and whitespace are optional and can be ignored.
All relevant key presses that occur during runtime (even when the application is not in focus) have to be saved in a log file that can be read and verified using any text editor (even an esoteric one, as long as I can verify it using that text editor).