For those of us in high population dense areas I recommend this (if you don't have a massive foaming at the mouth dog)
12 GA BLANK TRIP WIRE NOISE ALARM : Survival Gear at GunBroker.com
Reason is this, I've been discussing this with a few people and we've been wondering what would happen after initial food stores run clean (which all estimates say the food in your house and at stores currently will last the population eight days max). Once that's over with, people that aren't prepared are going to have to look for food, and chances are, they'll be looking at you.
Assuming you have no power, your security system is not going to be on and motion detection lighting is now useless. It'll be pitch black with nothing to alert you that someone may be trying to break in or even scope out your place. A handful of these inside and outside would not only scare the living crap out of an intruder but REALLY give you a heads up to grab the boomstick and be on the ready.
Just my two cents.