Want a key combination to lock the Mac screen like CTRL-ALT-DEL? Posted on July 8, 2010May 30, 2014 by happyorright LockTight for Mac OS X Intel gkoya. Is the answer. It is free and even works on Snow Leopard. I have used it and it works great and helps people who are used to the Windows way of using the keyboard to lock the screen more intuitively.