Skip to content

How Blind-Spot Monitoring Systems Work

A car's side mirror with a blind-spot monitoring system.

Drivers in cars equipped with blind-spot monitoring systems (BSM) have a distinct advantage over those without this popular safety technology. These detection systems alert drivers with a visual warning if there are vehicles occupying adjoining lanes outside their usual range of visibility.

Here’s a look at how these systems work and what you can do to protect yourself even if your car isn’t equipped with a BSM.

Monitoring Road Traffic With Sensor Technology

Blind-spot monitoring systems rely on sensors to detect approaching vehicles. The first such system was developed by Volvo Cars and deployed in 2003. Since then, every manufacturer has adopted the technology, although it may not be available with every make, model and trim.

Manufacturers install either radar or computer vision sensors to detect other vehicles occupying the left or right blind zones. Automakers may use different terminology to describe these systems, including blind spot information systems (BLIS), side blind zone alert and blind spot assist.

When a vehicle enters one of the zones, a visual alert typically appears on the corresponding side-view mirror face. Some manufacturers place the alerts on the inside of the front roof pillar nearest the mirror, or on an adjacent window frame. The alerts are usually an icon designed to show a vehicle approaching. Typically, the alert light activates and remains on as long as a vehicle is within that zone, which extends far enough to cover the adjoining lane.

Blind Spot MirrorCameras or sensors are located underneath or at the corner of each side mirror. Some systems also include bumper-mounted sensors. Together, the monitoring system components detect when a vehicle enters the blind zone and then send an instantaneous digital signal to create the alert.

Keeping the monitors and cameras clean is important to ensure the system’s effectiveness. Make sure you remove snow, leaves and other blocking debris that can render the system ineffective.

Bundled Driver-Assist Technologies

Blind-spot detection systems in new cars are typically bundled with other advanced safety technologies. Indeed, it isn’t uncommon to find blind-spot monitoring with rear cross-traffic alert, which drivers can use when backing out of a parking space to determine whether traffic is approaching from the sides.

Furthermore, some systems add lane-keep assist with lane-departure warning, a technology that not only detects an approaching vehicle in your blind spot, but also activates an audio warning and, in some cases, directly intervenes by nudging your vehicle back to your lane. As you may correctly surmise, the advanced technologies further reduce accidents, but should never be relied on exclusively.

The next time you shop for a vehicle, find out if it comes with a blind-spot monitoring system or other advanced safety technologies. If you don’t have such a system in your current ride, installing a set of blind-spot mirrors on your side mirrors can also reduce your chances of getting in an accident. Such mirrors extend your area of visibility, enabling you to visually check for vehicles as they enter your blind zones.

Check out all the relays, sensors and switches available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on blind-spot monitoring systems and blind-spot mirrors, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

Matthew C. Keegan View All

Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.

Leave a Reply

Your email address will not be published. Required fields are marked *