How to get Key Press By known person with UserInputService?

Of course if you:

print(game:GetService("UserInputService"):IsKeyDown() --a Random KeyCode Here

then you'll get that someone pressed a key. But who? How to find out who is pressing the keys? It would be useful, 'cause Getting Keyboard Input works bad, so I wanted to replace it with this.

Thanks,

SwaggyDuckie.