For many people home defense begins and ends with passive security measures. Passive deterrents certainly serve a function, but it should not be your entire defensive plan.

Locks The simplest passive defensive measure. Locking the doors to the house or the car increases the time and effort necessary to gain entry. Notice that I did not say that they keep people out, they merely separate those who are willing to make the effort from those who don't. Locks are basically primitive alarm systems, the noise of the breaking door alerts you to trouble.

Home Alarm Systems These are just door locks with a telephone and horn. Unless the secret code is entered in a timely fashion the horn will sound and the security company will be called. They will probably dispatch somebody to take a look at the crime scene, but not much more. If you were expecting SWAT to fast rope into your back yard you will probably be disappointed. That is not to say they are useless, so long as you remember to engage the perimeter alarm when you are home.

Dogs Depending upon the type and disposition of the dog, this might be an active defensive measure but generally you count on your dog to raise a ruckus if anyone approaches.

Outdoor Lighting This basically keeps people from using the cover of darkness to make approaches to your home. It is not a bad idea, just make sure it is installed in such a way that it can't be disabled during the daylight hours by an intruder coming back at night.

Indoor Lighting on Timers This is some of that folksy wisdom to combat people that want to steal your stuff when you are not home. It isn't particularly helpful one way or another.

Personal Alarms These are small noise makers that, in their intended role, you activate them when you are attacked and hope that someone better prepared than yourself arrives to save you, or that your assailant is terrified of loud noises. They have some utility for alarming the door to your hotel room, but otherwise serve no defensive purpose. Little kids love them to set traps for each other.

Rape Whistles When was the last time you went to investigate the sound of a whistle? Unless you can see the person blowing the whistle it probably doesn't register as an emergency signal. These are basically wind powered personal alarms and are useless.

If I left anything out please leave a comment.