Let me paint a picture for you: Last week. 9 PM. Outside my apartment building. I was rummaging through my backpack for a full minute before resigning myself to the inevitable: I had lost my key. There was nothing left to do but call my super, but as I pulled out my phone, I saw that my battery was at 9%. What if it died before I managed to get ahold of him? If only I had known about this simple trick.

Turns out, not all hope is lost when your phone is almost drained but you still need to use it. iOS 9 doesn’t just come with new emojis. It also comes with a feature called “Low Power Mode.” You can turn it on by going to Settings>Battery>Low Power Mode, or telling Siri to do it for you. It’ll immediately disable all those things that are sucking away your battery, including things you didn’t even know about.

For instance, you screen won’t automatically light up when you receive a text message. It changes your mail from “push” to “fetch.” It turns off motion effects and perspective zoom, and stops background apps from refreshing or automatically downloading. While you can toggle any one of these features in your settings, this new mode disables all of them at once.

This is such a simple feature, but it can allegedly extend your battery life for up to four hours. That’s enough time for me to call my super, order a pizza, and move up a few levels on Candy Crush. Problem solved.