I have a hearing impaired worker that I would like to be able to send SMS text messages for alarms, operator requests, process state, etc. I am thinking of using a GSM modem and I see a few out there, but I have no experience with any of them or how this would be set up. I am familiar with PLC coding and I am confident I can set up message "triggers" in the PLC code, but I don't know what the interface would look like to transmit text based on these triggers. Does anyone have a suggestion for hardware/software or experience in this area that can offer advise? I am running a Siemens S7-400 PLC.