It is just hours before Apple Inc.'s major fall event kicks off in San Francisco but we are still getting details of what the iPhone maker will announce, and one new feature could make controlling Siri a whole lot easier.

It should have been obvious from the tagline of Apple's event invitation, which reads: "Hey Siri, give us a hint," but it is Apple news website 9to5Mac, which has uncovered the fact that Apple's new iPhone 6s will allow users to control Siri simply by saying the phrase "Hey Siri" even when the phone is not connected to the power supply. Currently, to activate Siri on your iPhone or iPad you can either hold down the home button or use the phrase "Hey Siri" but only when it is connected to a power supply.

According to Mark Gurman, who has many reliable sources within Apple, the new feature will allow iPhone 6s and iPhone 6s Plus users to control Siri with their voices at all times. Requiring your iPhone or iPad to be connected to a power source significantly limits the usefulness of the feature in its current form, and by freeing up users, Apple will be hoping to see a significant uptick in usage.

Apple is also expected to launch an iPad Pro and iPad mini 4 at the event on Wednesday, Sept. 9, but it is unclear if the new always-on voice control feature will be extended to these devices. It is also unclear if it will be available on older models through a software update.

Siri Overhaul

Siri is getting a major overhaul in iOS 9 that will coincide with the release of the iPhone 6s and iPhone 6s Plus, which could be one of the reasons Apple has included the new feature.

The iPhone 6s and iPhone 6s Plus are part of Apple's 'S' update cycle and as such won't feature any major changes on the outside, though there are significant updates expected internally, including a faster A9 chip, improved cameras, 4K video recording, Force Touch controls, and better wireless connectivity while the big update externally is set to be a new Rose Gold option.

The ability to control your smartphone with your voice is nothing new and Motorola's Moto range of handsets have had this feature for a couple of years already with Moto Voice. Apple is seeking to play catch-up in terms of artificial intelligence with Google Now and Motorola's Cortana -- both surpassing Siri in terms of features and to this end, Siri in iOS 9 will offer users suggestions based on location and time using a feature called Proactive.

Apple typically doesn't comment on rumor or speculation but with the launch just hours away we won't have too much time to wait to see exactly what it is launching.