you want 2 alarms. One An easily visible deterrant alarm for when you open the door to either scare off thick CHAVs and/or to waste the time of a professional thief so they spend the 10 seconds it takes to rip it off and smash it. That will give your second alarm time to send you a text.

You could build an SMS based alarm system yourself and use a power invertor on a 12v car battery. You could add a small solar panel to lengthen the battery life (small alarms dont draw much).

But remember you need to check on it regularly to swap battery with a spare.