It's two-way: https://support.apple.com/en-us/HT213426 https://support.apple.com/en-us/HT213426 "Once you’re connected, your iPhone starts a text conversation

It's two-way: https://support.apple.com/en-us/HT213426 https://support.apple.com/en-us/HT213426 "Once you’re connected, your iPhone starts a text conversation with emergency responders by sharing critical information [...] You might be asked to respond to additional messages. Only Latin characters (such as English or French) are supported in these messages. [...]"