How do you make a notification or icon to appear on the map, telling other user that a user is facing a emergency and needs help?

[SteveJG]

@chang_jun

for this map screen, my user gets to alert the surrounding user that he/she is facing a emergency

What you want to do is to send a notification or message to nearby Android devices? It is not possible to send a notification/message to just people near you Sorry.

If you know the phone numbers or email addresses of those surrounding you can send text messages to those phones. Perhaps that is what you want to do?

Here is a way to send a text (sms) message to a single phone with your gps coordinates. How to text your Location to a Phone and Display the Location on a Google Map .