This feature will work irrespective of your data connection status.
Google is making it easier for users in difficult situations to communicate their need for emergency assistance without speaking to an operator. The new feature will allow those in a dangerous or emergency situation to simply tap on their screen to seek immediate help.
By tapping on the "Medical", "Fire", or "Police" buttons during an emergency call will convey the type of emergency along with the location details through the automated voice service for timely assistance, the official blog explains.
This feature will work irrespective of your data connection status. Google will roll out the feature in the Phone app on Pixel and select Android devices in the US over the coming months.