One of the new Siri-related features Apple introduced in iOS 8 is the “Hey Siri” hotword that gives a device always-on listening abilities when it’s plugged in and charging.
The feature doesn’t work when an iPhone or iPad is disconnected from the power supply, likely a measure meant to conserve battery life, but iDownloadBlogreports there’s a way to enjoy “Hey Siri” all the time, without having to charge the device at the same time.

Apple CEO Tim Cook speaks about iOS 8 at the Apple Worldwide Developers Conference in San Francisco, June 2, 2014. Apple has stopped providing an update to its new iOS 8 mobile operating software, following complaints by some users who said Wednesday, Sept. 24, 2014, that the update interferes with their ability to make phone calls. AP Photo/Jeff Chiu, File