On an iPhone 8 or above, continuing to hold these buttons down will sound an alert and start a countdown from three, and if the buttons remain pressed the call will be made automatically. iPhone users can also say the number 14 to the voice assistant Siri, which will then ask whether you want to make an emergency call – although in some countries it will connect straightaway.

https://www.bbc.co.uk/news/technology-56373292