Using a letters with KeyisDown

I’m making a space shooter, with ship movemnt control using the arrow keys. I also have a shield button that is currently the CONTROl key. When playing the game online their is a conflict with Flash Player. Flash Player has a shortcut that is left or right arrows + CTRL key. I want to use the key S instead, but for the life of me can’t figure out how to do this. My current code is:

if (Key.isDown(Key.CONTROL)&& _root.shieldStatus>0){

What would it be if I wanted to use the letter S, instead of CONTROL?