I didn't have an alarm at the back door because I had my yard surrounded by a fence and the fence usually works. The burglar attempted to steal my shower and I called the police and the burglar was arrested before they could get away with anything else. Sometimes I have had cases where the alarms don't work but I'm wondering if that happens when something is blocking it, like a fence or something. I try to put my alarms in places where nothing is blocking it. Sometimes a glitch occurs too where the burglar is standing outside my house after an attempted robbery and the alarm is going off and the police say "sorry the burglar got away" and he's still there but the police leave and the alarm is still going off because the burglar is there. It's annoying, because the alarm is on and my sim's won't sleep until it's off. Sometimes I call the police again and it scares off the burglar.
It's weird in my fence situation. The burglar will be walking up to my house and go up to the fence and suddenly be pushed through the fence. BTW, I don't usually use gates that give easy access to the house so I'm definitely not complaining that the burglar went into my house and I had a gate, giving easy access.