What is almost as bad as having no home security? Having a security system that constantly alerts on false positives! What are false positives? It is when you have a security alert, but it turns out to be nothing – like a stray dog or cat. For example, let’s say you have a fenced-in yard and an outside dog. You decide to install motion-sensing lights that turn on whenever motion is detected. There is only one problem – the lights go on whenever your dog moves around. That is a false positive since you don’t want the lights to go on because of your dog. After a few weeks of these annoying lights, you’ll either shut them off or ignore them. These two choices are wrong if you care about security. Unfortunately, that is the cost of false positives.
Other technologies have similar problems. Imagine a delivery driver leaving a package at your door. From the time the delivery guy shows up, drops off the package, and then leaves, you get 15 alerts. That would be annoying. To prevent multiple alerts, some doorbell motion-sensing cameras have a “cool down” period of a minute or so after they detect motion. For instance, a delivery guy shows up on the porch, scans the label, and rings the doorbell. Since no one is home, he drops the package off on the porch, walks away, and gets back in his vehicle. The doorbell will only send one alert on first detecting the delivery guy. The doorbell camera won’t send another alert from motion until the “cool down” period expires so they won’t send multiple motion alerts for the same incident. Basically, the last motion the doorbell detects starts a “cool down” timer. Once the timer expires, the doorbell will send a new alert if it detects motion because it believes this motion belongs to a new incident. Some savvy porch pirates know this fact. They hide, and right after the delivery guy leaves a package, they swoop in and take it. You are unaware of this event because it happened during the “cool down” period when the doorbell thinks the motion is part of the same incident, so it doesn’t send an alert.
Some technologies use Artificial Intelligence to determine whether motion is a pet or a person. You can select which one will send you an alert. However, many of these devices must connect to the Internet and send the footage to be analyzed. Depending on the server’s load, you may see several seconds or even longer delays.
As you can see, some devices try to reduce false positives. However, the best way to reduce false positives is to set up your home security with this reduction in mind. Let’s go back to our fenced-in yard and dog. Rather than install motion lights, I would likely put break beam sensors between the fence and the porch, probably around four feet high. If you read my book, you know I love Dakota Alert products. Their receivers have a relay output. If the break beam sensors trip, an alert will sound, and a relay can be triggered. That relay can turn out my outside lights and light up my house like a stadium (if it is at night). When I hear an alert, and my exterior lights come on, I know something broke the beam between my fence and my porch that was at least four feet high. It is something I should pay attention to.
Z-Wave is another technology you can put to use. Let’s continue our example, but now let’s say we also have a wrap-around porch. On the ceiling of the wrap-around porch, I may put some InfraRed (IR) motion sensors by the doors and windows. If this sensor is tripped, I can trigger large porch lights, the break beam sensor lights if they are not on, and many other things. A further example is if the time of day is between 11 pm and 4 am, I may want a siren to sound if the break beam lights and porch lights have been triggered. In short, there is a lot of capability in these systems.
Defense-in-depth applies here, too. Should a burglar get past your break beam and motion sensors on the perimeter, your alarm system will take over (you do set your alarm to STAY when you are home, right?). Door, window, and glass break sensors all come into play here. However, a significant design goal with perimeter defense is the reduction of false positives without the reduction of true positives. Please spend some time thinking about it and test, test, and test some more!