A video explaining how to use the new car crash detection feature on the Apple Watch is available on Apple's website.
The crash detection feature is designed to detect severe car crashes, such as front-impact, side-impact, and rear-end crashes that involve sedans, minivans, SUVs, pickup trucks, and other passenger cars. The feature can't detect all crashes.
If a car crash is detected, users will use the Apple watch. Users interact with the phone
An alert and alarm can be sounded when a car crash is detected. If a user is able to call emergency services, they can either dismiss the alert or use the Emergency Call feature on their phone. If they don't respond to the alert within 10 seconds, the device will start a new 10-second clock. The device will call emergency services if they haven't responded yet.
The car crash detection feature uses sensors on the phone or watch to detect crashes. In a press release, Apple said the feature uses advanced Apple-designed motion algorithms trained with over a million hours of real-world driving and crash record data.
Important safety considerations are outlined in Apple's video and support document.