If you've installed the app on multiple devices and in contact with their (devices) at a distance less than, for example, 10m from each other, is a graphic and sound alert.
How to implement such ideas?
Apparently, we need the remote server where to send the coordinates from the application. There they will somehow catch up?
Is there any ready solutions? Have basic knowledge in writing simple apps for this OS.
The way I see it:
1) Request permission to get coordinates
2) to Start the service and getting the coordinates
3) Send position to the server
4) If the coordinates on the server are close to each other to send a push on both devices
5) to push on the device and inform the user