Explanation:
Option 1: We cannot say that every visitor will be a thief or criminal. So a "home security system" is to stay alert from danger
Option 2: Burglars and home security system is to alert authorities and to protect our valuables. But home security system in addition can detect flood, fire, etc.
Option 3: Yes that's true. We feel like there is someone to protect us and our valuables. So it provides peace of mind.
Option 4: Why should we keep the doors unlocked? It will tempt for crime to happen. So this choice is invalid.