Not sure of the point here. Unless you're somewhere fairly close to the phone, you likely won't hear it anyway and if you're that close, you'd SEE them picking up your phone. Is this a theft concern or a privacy issue? If it's theft, invest a few bucks in something like Smart Guard which gives you remote tracking, automatic backup, secret "phone home" and remote wipe. I've been using it for a while now and love it. Left my phone in a blues club one night and when I realized it was gone, I didn't know if it was the club or somewhere else. I quick check with my online account, pinpointed where it was at.
I see the value in it. I may not be around but If I leave my phone on my desk and someone picks it up to take it or even just trying to be nozy, if an alarm starts blaring you can bet they are going to put it back down and they certainly aren't going to walk down the hall with it going off.
In my mind this is something you install in addition to eGPS (or Smrtguard). It's also something you use in conjunction with locking the device. The workplace really is a perfect example of where this would be useful.
Posted from my CrackBerry at wapforums.crackberry.com
I played around with a free one a while back called bWatchDoggy. It had a loud dog that barked and growled when you picked the storm up (until you swiped it a certain way). It was fun to mess with the kids with for a while, but I just used it as a gag, not security. Here's a thread on it, but I don't see it in the app store any more. You might be able to find it floating around somewhere still, though...