A head-up display (HUD) enables drivers to see all the details they need while driving without any hassle or risk of distraction (not to mention giving one's car the snazzy sci-fi feel of having data projected onto the windshield). Your car may not have included the technology, but that doesn't mean you can't easily equip it with its own HUD feature, and fortunately there are multiple ways to do this.
With a Smartphone and App
The easiest way to add a HUD to your car (or test out whether you like the technology before investing in a different option) is via a HUD app. After downloading and firing up the app, a driver simply puts their smartphone on the car's dash, and its reflection on the window serves as a distraction-free way to navigate.
If you're using an Android handset, there are several options available via the Google Play Store, such as the Navier HUD Navigation Free app, Vision HUD, and Car HUD. Many apps are also available for iOS users, including Awesome HUD and aSmart HUD+.
Using a Dedicated HUD
If using your smartphone or tablet as a HUD seems like a bit too much of a hassle, investing in a dedicated HUD device will provide you will all the information you need, no toggling devices necessary. A HUD unit has its own transparent display that is positioned near the driver, which displays the same projected information you'd get using a HUD app.
Many HUD units are available, with one example being the Garmin HUD, which we went hands-on with late last year. Options exist for motorcyclists, as well, such as the NUVIZ Ride:HUD that was crowdfunded last year.
This option has two possible limitations: the general lack of smartglasses on the market, and legal contention about whether wearing something like Google Glass while driving is allowed. While the issue of driving while wearing smartglasses is still in its infancy, that hasn't stopped apps that serve as HUDs from cropping up. The Glass HUD app might be the most notable in this category currently, though more options will no doubt be available in the future.
If you've gotten your hands on a pair of Glass, it could prove the most convenient option, always presenting information in your field of view regardless of where you're looking, and without the hassle of supplying power to a dedicated HUD unit. Be sure to check driving laws in your location before going with this option, however.