If you have an iPhone and are ever in a dangerous or threatening situation, rapidly press the lock button 5 times (iPhone 7 and earlier) and you will see this screen. Then, swipe the SOS and you'll be immediately connected to 911.
If you have an iPhone X, iPhone 8 or iPhone 8 Plus, press and hold the side button and one of the volume buttons until the Emergency SOS slider appears.
Click here for more info: http://www.ktvu.com/news/how-to-use-emergency-sos-on-your-iphone
Check out Jack and Carolyn's podcast, here: