Let's start with a little background: Nearly any carmaker's marketing department will tell you that its cars are born from jets. But the heads-up display is the most prominent option that actually comes from the aviation world. First patented by the Royal Air Force during World War II, it enabled the to fly faster and easier at night. As jets evolved, so did advancements in instruments, flight computers, and guidance systems. HUDs have become essential to flying. In a fighter plane, with the enemy on your tail and AIM- at the ready, having all that information right up front could mean life and death.
How does it work?
Your windshield serves as a giant screen, and a projector embedded in the dashboard sends a transparent image onto it. The image leaves the projector and bounces off a series of mirrors, magnifying and flipping the image so that the data comes out right-side up and legible. Press a toggle switch by the dashboard and you can adjust where the display is on your windshield—something accomplished with a rotating mirror.
Some car companies like Mazda project their heads-up data onto a small plastic window that flips up, known as a combiner. This creates a uniform image no matter how the windshield's shaped. It also reduces the number of mirrors needed to send the image onto the windshield clearly. And a lot of aftermarket displays use such a combiner so you can install it in nearly any vehicle you please.
What can you see?
There's your speed, sure—that's the most important one. And turn-by-turn navigation, complete with ghostly arrows all floating right atop your lane. The Corvette has had an HUD system since 1998, and it displays performance data like engine speed, g-forces, gear position, and oil temperature, further reinforcing that fighter-pilot cachet. And on some high-end cars, there's even the option of night vision: projecting images taken from behind the grille onto the windshield, it may save you from running into animals.
Further on down the line, manufacturers aren't just calling it a mere Heads-Up Display. Rather, it's full-on augmented reality—arrows and pathways overlaid on the road ahead, providing foolproof navigation, and the ability to see how fast that truck is going in front of you, and if there's anything behind it you might miss. Companies like Continental and Harman are working on this right now.
So the takeaway? If you think your car is too old or plebeian for HUD, know that the cheapest HUD system on ("Modernizes your vehicle!" says one five-star reviewer.) These systems plug into your car's on-board diagnostics, and mine it for every bit of data you might need: speed, fuel consumption, mileage, engine faults, everything except navigation. It's easier than you think to retrofit your ride.