If you're like me, you spend a fair amount of time looking for your iPhone. Did it fall between the couch cushions, or is it still in a pants pocket?
Marco Polo (US$0.99) can solve that problem and find your iPhone in a jiffy. When you run the app it stays in the background listening for the phrase "Marco". When it hears that word, it responds "Polo". It's simple, and pretty effective.
I tried Marco Polo around the house, first putting the phone on a dresser. That was an easy one -- I said "Marco" and the phone replied. I also put the iPhone under a couple of blankets, and that worked too. Then I put my iPhone in a drawer in the kitchen, and while the sound was muffled, I could hear it respond. Obviously, if I got too far away -- like two rooms away -- it wouldn't trigger. But I would be quite happy to shout out a couple of different "Marco's" to find my lost phone.
There are some customization settings. You can type in another word besides "Marco" to use to trigger the response, but the phone will always say "Polo". The response voices can be customized too, which is a nice touch.
The app doesn't require an Internet connection to work. There is an option to use the loudest volume your device is capable of when responding, even if your iPhone volume is set to its lowest setting. Marco Polo is tuned to North American English for now, but other dialects may be coming.