What Is a Blind-Spot Monitor?

Photo: Witthaya Prasongsin/Moment via Getty Images

Blind spots are the areas to the rear of a car on either side that are not readily visible to the naked eye or in a car’s mirrors. If you drive, blind spots are a fact of life. Fortunately, blind-spot monitors or warning systems are here to help you see what may otherwise be blocked from your view.

Some drivers might think they don’t need any sort of fancy technology to help them see their blind spots. While it’s true that the mirrors of most cars can and should be adjusted to minimize blind spots, every car, truck or sport-utility vehicle is going to have them to some extent. These days, many popular vehicles have large pillars between the body sides and roof — whether for safety purposes or just for style — or sloping roof lines that can block a driver’s view. If you own a truck or SUV with a tall or heavy-duty suspension setup, you may have a limited view of what’s behind you, especially if it’s a comparatively small vehicle.

Even if your car has great visibility and you have your sideview and rearview mirrors perfectly adjusted, a visible or audible warning letting you know that there’s a vehicle approaching your blind spot can be an effective safety measure. That’s why blind-spot warnings are so handy. These systems constantly monitor a car’s blind spot and alert you to dangers you may not otherwise see.

How does a blind-spot monitor work?

Blind-spot monitors are part of a modern car’s advanced driver assistance system (ADAS) and can include several different technologies to detect motion, including radar, cameras or ultrasonic sensors. These exterior sensors are combined with an additional interior component, usually a bright light or some sort of obvious icon, that’s easily visible from the driver’s seat. When the blind-spot warning system detects another vehicle currently in the car’s blind spot or one that is quickly approaching from behind, an illuminated alert tells the driver that it’s not safe to change lanes. These alerts are commonly seen on the car’s side mirrors or on the pillar to the left or right of the windshield. 

If the driver activates a turn signal or starts to veer into the adjacent lane, the car escalates the warning. The next phase of blind-spot alert may include audible beeps or a haptic shake of the steering wheel or seat.

ADAS can also include additional technologies connected to a blind-spot monitoring system to improve safety. Your car may have a video image that’s displayed in the instrument cluster or infotainment screen when a turn signal is activated, giving a visual view of your car’s blind spot. Some vehicles may actively use the steering or brakes in an attempt to keep a driver from changing lanes when there’s another vehicle in the way.

Technologies like lane keeping assistance, lane departure warning and cross-traffic alert may use the same sensors as the blind-spot monitoring system and be integrated into a broader safety package.

Are blind-spot monitors effective?

The Insurance Institute of Highway Safety (IIHS) reported in 2018 that blind-spot warning systems reduce lane-change crashes by 14%. They also result in a measurable reduction in the number of collision claims made to insurance companies and police reports of injuries, according to research from the Highway Loss Data Institute. The National Highway Traffic Safety Administration lists blind-spot monitors among its recommended safety technologies.

In a survey of the owners of around 47,000 cars built between 2017 and 2022 and equipped with advanced safety systems, Consumer Reports says 64% of respondents were satisfied with their blind-spot warning technology.

Put simply, blind-spot monitoring technologies make our nation’s roads safer for all drivers.

Are there any drawbacks to blind-spot monitors?

Having the help of sensors to alert you of impending danger is great, but ultimately you as the driver are always responsible for safety when behind the wheel. If you get accustomed to relying on a blind-spot warning, you could become lax to the importance of paying attention to the road ahead and using your eyes to visually scan for vehicles behind you.

Many blind-spot monitoring systems can be turned off using either a button or the in-dash screen. Overactive alerts can be a distraction that drivers choose to ignore or disable.

Safety systems that rely on cameras or sensors need to be kept clean to work properly. Adverse weather conditions like hard rain, heavy snow or fog can reduce their effectiveness.

Blind-spot monitors tend to work best at highway speeds, meaning their effectiveness around town can be reduced. They may also have a harder time recognizing small vehicles like motorcycles and bicycles than large ones like cars and trucks. Pedestrians or animals in a vehicle’s blind spot are even less likely to be spotted.

An accident can damage ADAS technology, including blind-spot monitoring, which can increase the cost of repairs. A report from AAA in 2018 found that repair costs of cars equipped with advanced safety tech can be double or triple that of cars without such systems. A survey of vehicle owners by the IIHS found that some had continuing problems with safety technologies even after they were repaired, requiring more than one trip to the shop to get them fixed and working properly. Despite such issues, most owners still said they preferred having them.

Popular automakers that offer blind-spot monitoring

Every automaker that sells cars in America offers some sort of blind-spot monitoring technology, but not all systems are equal, and almost none of them share a common name. Groups that focus on automotive safety and the ownership experience such as Consumer Reports, AAA, J.D. Power, the National Safety Council, Partners for Automated Vehicle Education and SAE International are working to get automakers to adopt a list of standardized names for advanced safety systems, but so far they have not been adopted by major automakers.

With that out of the way, here are the names that popular automakers use for their blind-spot monitors along with links explaining how they work.

Acura, Honda: Blind Spot Information
Audi, Volkswagen: Side Assist, Blind Spot Monitor
BMW: Blind Spot Detection
Buick, Cadillac, Chevrolet, GMC: Side Blind Zone Alert
Chrysler, Dodge, Fiat, Jeep: Blind Spot Monitoring
Ford, Lincoln: Blind Spot Information System (BLIS)
Genesis, Hyundai, Kia: Blind Spot View Monitor
Infiniti, Nissan, Mitsubishi: Blind Spot Warning, Blind Spot Intervention
Jaguar, Land Rover: Blind Spot Assist
Lexus, Toyota: Blind Spot Monitor
Mazda: Blind Spot Monitoring
Mercedes-Benz: Blind Spot Assist
Mini: Blind Spot Detection
Porsche: Lane Change Assist
Subaru: Blind Spot Detection
Tesla: Blind Spot Assist
Volvo: Blind Spot Information System (BLIS)

Can you add blind-spot monitors to an older car?

Sort of. Some aftermarket companies offer blind-spot monitoring technology for cars that weren’t originally equipped with it from the factory, but installation may not be simple. Multiple cameras or sensors may need to be affixed to the exterior of a vehicle, all of which then need to be properly wired together. Such systems may require a professional to install and calibrate to ensure they work as intended.

There’s at least one potential low-tech and low-cost alternative. Large exterior mirrors with multiple angles or convex lenses can be fitted to some cars or trucks, especially those that are used to tow campers or trailers. They may not be as effective as a true blind-spot warning system, but these kinds of mirrors can help you see areas that might otherwise be in your blind spot or blocked by what’s hooked to your hitch.