The waiting 30 seconds part screws the usefulness. I am thinking of cases where say, someone leaves a garage door open and they don't lock their car, it would be nice to have the security go off is someone attempts to enter without the FOB.

I am screwed by this one thing: I grew up in an area where locking cars and houses was just not done -- there was never any crime. Where I live now, people will steal your plants if left outside.