A few years ago there was a TV show on the Discovery Channel called "It Takes a Thief" where a former burglar would demonstrate how easy it is to break into the average American home. A couple of points I remember about the series was that a professional thief would bypass a house that had a dog or a security system because there are plenty that have neither. A pro can probably tell if a building has an active system or just has a sign or sticker on the door. Once someone on the show had their home "burglarized" (the host would show how quickly he could find and cart off their valuables), they would get a complete security makeover, which included new door and window hardware and an alarmed security system. Then after a few weeks, he would try to get back into the home and was successful in about half of the attempts because the family would leave a window open or forget to arm the system.
It was always interesting to me to see how quickly he could determine if a home was vulnerable and how easy it was for him to get in. He would then take everything, including cars, credit card information, jewelry, heirlooms, and guns within 10 minutes. If the homeowner had an unusual name, and it's displayed on your mailbox or property, he could call information, get the phone number, and telephone the house to determine if they were home. Bushes, fences, and other obstacles provided cover from prying eyes and he did all of his break ins during broad daylight. If the house was in the open or had a security system sign on the property he would simply bypass it for an easier target, though it could easily be determined if it were just an empty threat. They would know what to look for, such as contacts on the windows, specific wiring near the electrical meter, or an alarm panel next to the door, so I wouldn't trust the safety of my family or my stuff to a window sticker without an actual alarmed system.
An alarm is just part of the system, too. Safes that contain all your important papers and other small valuables, solid doors and windows with good hardware that are all locked, upstairs windows that aren't easy to get to by people who are agile and determined to get into, and not leaving highly personal information in the open and unlocked. They showed all of that and more in the two seasons the program aired. It always amazed me that people would get a free security upgrade and then about half of them would forget to use it properly, at least when the hosts made a return visit. A security system is kind of like health insurance or a good diet. It only works if you have it and continue to pay for it, though there is no immediate benefit that is easily determined. It's like the old joke about the two guys who are hiking in Alaska and they come upon a grizzly bear. One of the guys takes off his boots and starts putting on his running shoes. His friend says, "What are you doing? You can't outrun a grizzly bear". He replies, "I don't have to outrun the bear. I just have to outrun YOU." Same with a security system. They aren't infallible, but they are a deterrent, and are extremely hard to bypass if used properly.
Long time homeowner and have worked in a large metropolitan area for many years and had some security training.