Anxious To Install New Security System

I used to have a security system, but I let it lapse. I was always setting off the alarm by accident and chancing getting penalties for doing so. Then the batteries died, and the whole system went haywire. It was going off with nonstop shrieking sirens. Enough, I had them snip the wires. Couldn't stand it. However, now I am thinking I should get another alarm system, maybe one of those wireless alarms. I fell asleep on the sofa not long ago, and woke up at 5 a.m. when I heard a knock on the door. My blood went cold. I live in an urban area, and I do not want people knocking on my door at 5 a.m.