Your iPhone's Health app can store medical conditions, allergies, medications, and emergency contacts. Enable Show When Locked so first responders can access it from your lock screen without your passcode. This can save your life if you cannot speak.
On iPhone, press and hold the side button and either volume button until the SOS slider appears. On Android, rapidly press the power button 5 times. The phone automatically calls 911 and sends your location to your emergency contacts. Practice this so it becomes automatic.
On iPhone: Health app > Medical ID > Add emergency contact. On Android: Settings > Safety & emergency > Emergency contacts. Tell your contacts you added them so they know to respond.
Apple Watch (Series 4+) can detect a hard fall and automatically call emergency services if you don't move for a minute. Some Android phones offer similar features. Consider a medical alert pendant as an affordable alternative.