Hello Phil,
Thanks for letting us know about your situation.
To get SMS message record on your I/O parameter trigger you need to do few steps:
1. At your device configurator need to set at the System option Record Saving/Sending without TS set it at always
2. At your device configurator in the SMS/Calling option need to enable to allow SMS data sending write your Data sending number and write your number at GSM predefined number.
3. At your device configurator in the I/O parameters you set high priority on those parameters you want to get SMS message set low level, high level parameters and opperand and choose in Send SMS to combo box your number.
4. Save your configuration
When your I/O parameter will be triggered you will get a SMS message.
I will attache an example of configuration screen for you. In this configuration screen you can see that we have configured I/O parameter with external voltage and you will get a SMS message to pre-defined number if external voltage will be less than 10V or higher than 14V

Additional information about the opperands can be found in: https://wiki.teltonika.lt/index.php?title=FMB204_I/O_settings