The Find My iPhone feature that is part of Apple’s iCloud service is a great security option to enable, as it allows you to locate, erase, or message your device if it is ever lost or stolen. This service can be easily enabled for OS X or iOS devices, where once you have logged into iCloud in the OS X system preferences, you can check this option as one of the features to enable. In the case of iOS, you can toggle this option in the Settings > iCloud > Find My iPhone section.
This feature has its obvious security uses, especially for iOS devices that are quite easy to be stolen or lost somewhere. Even though in the case of theft, iOS 8 will lock your device to your Apple ID and thereby secure your data and prevent use of your device, in the event you simply misplaced your iPhone or iPad you might be more inclined to try finding it instead of wiping or locking the device.
In these cases, Find My iPhone comes in handy; however, this feature is only useful when your iOS device can connect with iCloud, and this is subsequently only doable if the device has power. If your iPhone or iPad is critically low on battery power, then it may simply shut off and no longer communicate with iCloud, requiring you to hunt it down without the Find My iPhone service.
To combat this, in iOS 8 Apple includes a slight augmentation to Find My iPhone, where you can have the device send out a last signal to iCloud in the event of a low battery, right before the device shuts off. You can then log into iCloud and will be shown the last known location of the device, and be able to at least have a better idea of where it is than if the device were to just power off with no communication at all.
I upgraded my 5s, and must admit, I missed this one, even though I’m pretty sure I remembered to go back and make sure it was turned on. Great reminder, thanks!