**Bash + Xdotool, 45 bytes**

    for((;;)){ xdotool key Num_Lock; sleep .5; }

Just execute it in a bash shell.  It needs to be in a graphical environment.  It uses Num Lock because it is shorter(Thanks to @Engineer Toast), and infinite loop from [here](http://codegolf.stackexchange.com/questions/15279/tips-for-golfing-in-bash)