I've a couple occasion where I have either misplaced my iPad/iPhone and used "Find my iPhone app to locate it". As long is it is turned on and the battery has charge, you will promptly find it. If it had been shutdown or the battery has run down, it will report where it was prior to either of these events.

One day I could not find my iPhone. The app said it was at my home. I tried calling it, but I had my ring in silence. I then sent out a signal from the app on my iPad to cause my iPhone to beep. Could not hear it. I then opened the doors on each of my cars and in one of them I could hear a muffled beep but still could not locate if. Finally found it between passenger seat and console where it had fallen.