From PopSci.com….
Emergencies are, by definition, unexpected, so it’s critical to know exactly how your phone can help when you need it most. Both iOS and Android have built-in capabilities that will almost instantly alert first responders, family, and friends to the fact that you need assistance.
If you fear pocket-dialing the paramedics, you can limit these settings, but you can’t shut them off entirely—federal law requires all phones sold in the US to be able to dial 911, whether or not they have an active SIM card or are linked to the available wireless networks. As long as your device can make some sort of connection, you should be able to call for aid.
Emergency call settings on iPhones
The fastest way to call emergency services on an iPhone is to use Emergency SOS. Fully enabled, you’ll be able to notify first responders without taking your device out of your pocket or bag—as long as you can grab your phone, you can fire off a cellular flare.
By default, an iPhone 8 or later model will call for help if you hold down the side button and either volume button. Do this, and the Emergency SOS slider will appear within seconds. Then, you can drag it to the right to make the call, or keep holding to activate a five-second countdown before the call goes out. You cannot turn this off. During the countdown, your phone will vibrate to let you know it’s working. Stop the countdown at any time by releasing the buttons.
