Siri just keeps getting smarter.

A new feature in iOS 9 will let you to train Siri so the assistant will only respond to your voice saying "Hey, Siri." The new voice recognition feature was rolled out in the new iOS 9.1 beta that launched Thursday.

Apple first added the hands-free "Hey, Siri" functionality in iOS 8. When enabled, the feature lets you initiate voice commands without touching your device when your phone is plugged in to a power source. In iOS 9, a new voice recognition feature allows you to "train" Siri to respond to the command from your voice only.

To enable it, toggle to Settings > General > Siri and select "Allow 'Hey Siri.'" Once enabled, you'll be prompted to go through a quick five-step process so Siri can "learn" your voice. It prompts you to say "Hey, Siri," three times and then asks you to repeat two additional commands: "Hey, Siri, what's the weather today?" and "Hey, Siri, it's me." The entire process takes under a minute.

Once you've finished, Siri is able to recognize your voice, Apple says. Again, while Siri has been able to respond to "Hey, Siri," commands since last year, she will now only respond to you once enabled in iOS 9. Sure enough, I tested it out with a colleague; no matter how many times he said, "Hey, Siri," my display remained locked until I was the one to speak.

New voice recognition is just the latest way Apple is improving Siri to make its assistant play a more important role

New voice recognition is just the latest way Apple is improving Siri to make its assistant play a more important role in iOS than ever before. In iOS 9, Siri will also provide what Apple calls "proactive assistance," such as predictive notifications based on information from your Calendar and Mail apps.

Siri will also be able to answer contextual questions, a feature that Microsoft's and Google's assistants have had for some time, and powers a number of new search features. Apple also opened up a new Search API to developers that will allow third-party apps to take advantage of Siri's new superpowers.

The new Siri features will be available beginning Sept. 16 when iOS 9 becomes available to download.