How to organize data transfer to an android device?

Question

Android

I say right away that I am not interested in ready-made solutions, but in technologies.
It is necessary in the local network (no Internet access) to transfer data to several android devices (from 1 to 30) in a small amount (small text, sometimes a picture) with a slight delay (no more than 10 seconds). For this, rational solutions are sought. There are two in mind:

1. Constantly working socket with screen shutdown lock. Eats the battery, but, as I understand it, it is possible to work in the background.
2. Push notifications. I'm not very familiar with them, but it seems to me that they cannot unlock the screen and launch the app activation.

In general, arguments are being sought for/against the above options and other options for organizing this kind of application.

Answer 1

ejabberd in conjunction with Xabber as a client - everything is already written and works great