With iOS 8, Apple has added another feature to make it easier to find your iOS device when it seems to have disappeared. The feature is called "Send Last Location," and as the name implies, it will automatically send you the last known location of your iOS device when the battery gets down to a low level. This is great because once the battery is drained, Find my iPhone is of no help. Knowing where your iOS device was before it ran of out juice, however, is a godsend.
To activate it, go to Settings > iCloud > Find My iPhone and then toggle on the "Send Last Location" button.