Blind-Spot Monitors: Everything You Need to Know

By Russ Heaps 11/01/2021 12:00pm

Blind-spot monitoring (BSM) is just what its name implies: It keeps an eye on the space just off the rear quarter areas of your vehicle. These blind spots can hide a vehicle approaching in an adjacent lane because many drivers improperly set their car’s outboard mirrors. Consequently, merging into that lane often results in a crash.

In fact, according to the National Highway Traffic Safety Administration (NHTSA), roughly 9% of all reported vehicle crashes each year result from changing lanes or merging.

BSM is an active driver aid/safety device with the ability to detect what your eyes may miss, issuing a warning as a vehicle approaches in an adjoining lane.

Once only found in high-end luxury cars, blind-spot monitoring eventually trickled down to even economy cars. If BSM isn’t standard on a vehicle, it’s probably available as a stand-alone option or in an option package.

The larger your vehicle, the bigger the blind spot. The bigger the blind spot, the more BSM can help prevent you from changing lanes into another vehicle.

What is Blind-Spot Monitoring?

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As far as today’s crop of driver-aid technologies goes, blind-spot monitoring is quite simple. The least sophisticated examples use radar or ultrasonic sensors embedded in each side of the vehicle’s rear bumper. These sensors detect a vehicle approaching the rear of your car in an adjoining lane. More sophisticated BSM systems also employ side-mounted cameras.

When BSM recognizes a vehicle about to enter a blind spot, it warns you that a particular adjoining lane is not clear. Commonly, the alert comes in the form of a yellow warning light somewhere on the outboard rearview mirror on whichever side of the oncoming car is involved. It may, instead, appear on your vehicle’s A-pillar (the pillar between the windshield and either front door), driver-information display, or head-up display.

A few brands, such as Honda and Kia, provide an audible alert in some models. Often, audible alerts will sound if you use your turn signal, indicating you will merge into an occupied lane.

How Blind-Spot Monitoring Works

Blind-spot monitoring eliminates some of the guesswork from effectively positioning your outboard mirrors because it acts as an early warning system for vehicles about to pull alongside you.

It uses a combination of sensors and sometimes side-mounted cameras to track approaching traffic in adjoining lanes. You can often spot the sensors. They are usually quarter-size round indentations in the bodywork or fascias.

Once BSM senses an advancing vehicle, it springs into warning mode. Some blind-spot monitoring systems are so sophisticated that they will nudge you away from the lane marker on that side. The system may even steer you back to the center of the lane.

Advanced Blind-Spot Monitoring Systems

As technology tends to do, blind-spot monitoring continues to evolve. When first introduced fewer than 20 years ago, BSM was a novelty reserved for premium and luxury cars. Today we find it on the most affordable of models. For example, it’s standard on the $19,500 Nissan Kicks S and comes with the $500 Technology Package for the $19,590 Kia Forte LXS.

As already mentioned, cutting-edge BSM versions that either nudge you away from the lane marker or steer you back to the lane’s center are also available in many cars. They accomplish this through steering or by applying brake pressure to one or more wheels.

Even full-size pickup trucks are getting into the act. No matter the brand, every full-size pickup has blind-spot monitoring either standard or available. The Ford F-150 and Ram 1500 pickup trucks take it even farther. They offer BSM that extends to the trailers they are towing.

Added Safety with Blind-Spot Monitoring

There is little question that BSM is one of those features we didn’t know we needed or wanted until carmakers began offering it. Volvo was the first, incidentally. It offered its Blind Spot Information System (BLIS) for the S80 in 2005.

With nearly 10% of vehicle accidents being lane-changing crashes, BSM can be a useful tool when utilized. In a 2017 article, the Insurance Institute for Highway Safety (IIHS) reported that blind-spot monitoring reduces lane-changing accidents by 14%. Moreover, it reduces injuries from lane-changing crashes by 23%.

Blind-spot monitoring often pairs with rear cross-traffic alert (RCTA), which uses the same sensing tools as BSM. Whether it’s backing into other vehicles or backing into people, a lot of mayhem occurs when backing up in parking lots.

RCTA comes to life when you shift into reverse. Less sophisticated systems monitor vehicles on a course to cross behind your car. When rear cross-traffic alert detects a crossing vehicle, it issues an audible warning.

More advanced RCTA systems also recognize pedestrians and sound an alert when a pedestrian is behind you. Even more advanced systems will sound an alert and automatically apply the brakes.

Tips for Using Blind-Spot Monitoring

To maximize the effectiveness of blind-spot monitoring, we recommend you:

Wipe off the cameras: Ensure the cameras and sensors are free of dust, mud, snow, and whatever else might interfere with their proper functioning. Clean them off and wipe them down.
Check your car manual for setup: Consult your owner’s manual for specifics on engaging and setting your active driver aids. That way, you can stay safe while driving.
Know the system’s limitations: Be aware of any limitations your particular system may have. Not every BSM system operates the same. Some may only function at certain speeds and so forth. Every blind-spot monitoring system doesn’t recognize pedestrians, cyclists, and pets.
Use your eyes: Before traveling in reverse, always double-check with your own eyes what is behind you.

Benefits of Blind-Spot Monitoring

We are convinced that if you haven’t experienced blind-spot monitoring, you will grow to appreciate it. Here are a few benefits you may not have considered:

It will prevent some accidents and can minimize others.
You will experience increased driving awareness.
You will feel safer and more confident, and so will your passengers.
Early warning increases the time you have to respond.
It relieves you of some of the stress of driving in close quarters.
The larger the vehicle, the greater the benefit.

Types of Blind-Spot Monitoring Systems

Currently, there are basically two types of blind-spot monitoring systems. The less-intrusive system simply provides an alert. The more intrusive system pairs the alert with steering assistance.

Blind-Sport Warning

Just an alert, this BSM system issues a visual warning usually found on the outboard mirror or the A-pillar on the side with the potential danger. More involved versions will also sound an audible warning if you engage the turn signal on that side.

Blind-Spot Warning with Automatic Emergency Steering

Such systems may also engage the brakes on one or more wheels to nudge you away from trouble. However, if you attempt to head into a lane already occupied by a vehicle, this system will not only issue a visual and audible warning but steer you back to the center of the lane as well.

Installation

Factory

If your vehicle has blind-spot monitoring, it most likely came from the factory that way. Built-in BSM is the more common system because it makes sense. The sensors are nearly seamless in a factory system and are exactly where they need to be for the most effective performance. The warranty covers the system and so does your auto insurance.

After-Market

There are some after-market kits out there that are ideal for older cars. Amazon, Walmart, and Crutchfield are three of the many retailers for after-market models. Expect to pay $300 to $500 for a solid system.

If you have a Saturday to invest, you might want to install it yourself. However, it’s a fairly involved process. Having a kit installed professionally will cost at least $200.

Key Features

The main features in an after-market blind-spot monitoring kit are the sensors and the indicators.

As with a factory-installed system, the sensors are the eyes of the system. Like your eyes, BSM requires at least two sensors (one for each side) to function. Usually either radar or sonar, the sensors will pick up an oncoming vehicle when it’s a specific distance from your car.

Once a sensor detects an approaching vehicle, it transmits an alert to the indicators. Most kits include warning lights and some kind of audio alarm as indicators.