Information privacy
What is it stopping a stranger from finding out every information about me using the emergency button without unlocking my phone
Hello DarkK,
Read this help document:
Use Emergency SOS on your iPhone - https://support.apple.com/HT208076
You will see all it does is call the emergency number in your country (911 in the USA), and optionally sends you location to your emergency contacts. I hope these are people you trust, and of course normally you would not care if they knew your location if you were in an emergency situation.
The feature is not letting anybody actually use your phone or find information from it. Perhaps just tell your friends if they call you as a result of getting a notice not to provide any information, just in case a person steal this phone and tries to pretend to be you.