How to connect few android devices?

There is restaurant, and I have wrote app for them. Now my task is to create device communication: only single app (on a single device) should work at one time. I.e. when user starts to use application on one device, apps on other devices should show warning "Please, wait...". How I can do this? I am thinking about creating lock-file on some server (maybe on dropbox open folder???). At start app should look to this folder and if the lock file is exists - wait. If there isn't lock file - 开发者_开发百科app will create it, performs all users tasks, delete lock file, and closes. Another idea - is to use bluetooth connection... Maybe at starting app should seek for bluetooth device with special name... if it isn't - open bluetooth communication with that lock-name and begin to work... But the problem is the device os 1.6.

I think you're on the right track, but maybe a little far down the development path to think of this now.

Anyway, create an exclusive lock that you expose in a webservice you've deployed on apache (obviously, that service will also expose an unlock method too).

Use a local wifi network (one you install in the restaurant) with a tiny linux box and you're in business.