After purchasing this, i found these also quite cheap:
Dick Smith Multipurpose Keypad Alarm - $2
Dick Smith Door Stop Alarm - $2
Dick Smith Slim Glass Break Alarm - $2
Dick Smith Slim Glass Break Alarm - 4pk - $5
Dick Smith PIR Alarm with remote - $5
Dick Smith Ceiling Alarm w/remote - $5
You can view them all here
Hopefully useful to someone :)
All of a sudden i have become an expert in security :)