Operating a computer to perform everyday tasks is sure to require input devices. The common human interface devices for operating a computer are mouse and keyboard. It means that modifying input devices can be alternative way to do monitoring and logging activity from a user. A keylogger is able to do such functions, but various hardware and software keylogger on the market are easily detectable either physically or by antivirus software. Those limitations can be avoided by hiding a keylogger directly into the keyboard. This key logger is implemented using Teensy 2.0 USB development board, which differs between the PS/2 and USB variant. Results of analysis shows that the keylogger in undetectable physically and works correctly just like any normal keyboard. The drawbacks are reduced performance as in increasing delay between held keystrokes, key ghosting and key jamming.