My current sim's first house had a fenced in yard with no gate. The only access to the yard was though the house. A burglar came to her house, and was spawned inside the yard. The burglar went through the house and out the front door, without stealing anything, and set off the burglar alarm just outside the front door. I assume he had to go inside the house through the front door before he could steal anything, but after that I put an alarm beside the back door too.
My sim moved to a new, much larger house later. On her very first night in her new home, a burglar came. As soon as he got into the first part of the yard through the celebrity gate, the alarm on the front of the house went off. He ran through the inner gate, to the main part of the yard, ran under the deck of the second story main floor entry, all the way to the back of the house, where there is another burglar alarm, near the sliding glass door to the ground level basement, and set off that alarm too. He waited there for the police to come. After the police officer sent him out to the patrol car, the officer changed into his swimwear, and climbed up on the pool slide to slide into my sim's pool. He acted like he was afraid, got off the slide and changed into his everyday outfit, without ever actually getting into the pool, went out to the patrol car and told the burglar to wait by the car, then went into my sim's house to check it, then finally took the burglar away in the patrol car.