Threshold is where the alarm goes off, if it is negative then that means the alarm is disabled. Click the "Enable" button to flip it positive, or just enter the temperature you want the alarm to go off. To have it send an SMS, your cellular provider has to accept the SMS from an email to text gateway, which means that the email bits have to work first. Always make sure to "Save & Apply" at the bottom of the page after changing anything and before you expect it to do something.