jQuery key code for command key

jQuery already handles that. To check if control was pressed you should use:

$(window).keydown(function (e){
    if (e.ctrlKey) alert("control");
});

The list of modifier keys:

e.ctrlKey
e.altKey
e.shiftKey

And as fudgey suggested:

e.metaKey

Might work on MAC. Some other ways here as well.