Hi guys. I'm going to develop an industrial application in which I need 4 Arduino devices to monitor 3 digital signals each and communicate via GSM. What I basically need to know is which kind of protocol (and shields) you suggest to share those bits between the 4 Arduinos considering that only one will have the GSM shield. Unfortunately only one Arduino will have GSM capabilities and no wired connection between them is possible. Max distance between them should be 10 meters, at least I hope no more... :) In case of Wi-Fi suggestions I have no problems in adding a basic router or something similar.
I hope you can help me since there's so much stuff I don't know which solution could fit at best this application.