I’m no expert at this. Reading an alarm input on the GPIO is probably not too difficult. It looks like 1-wire is supported on GPIO-4 for the Dallas/Maxim DS18B20 temperature sensor. Once you have the state or information, sending a email is not too difficult. I’ve got fetchmail, postfix, and dovecot running and can send emails from the command line.
Years ago there was at least one web site that allowed you to send free text messages. They are probably all pay services now or require a cell module connected to the R-Pi.
Let us know how it goes.