Putting your Mac to sleep from your phone is handy when you leave the room and forget to secure your computer. Blogger Rick Stawarz shows that it's easy to make this happen using the iPhone app, Launch Center Pro, then Dropbox and Hazel on your Mac.
Essentially, you'll make a folder in Dropbox that Hazel monitors for a key phrase. When a file shows up with that phrase, Hazel locks your computer and puts it to sleep using ActionScript. Then, in Launch Center Pro, you create a button that creates a new file with the key phrase in it. So, to put your computer to sleep, you can just open Launch Center Pro on your iPhone and tap the button. Within a couple seconds, your computer will be locked up and asleep. Grab the full directions over on Stawarz's site.
Remotely lock a Mac's screen with Launch Center Pro [Rick Stawarz]