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" Reach into your pocket and you&amp;#039;ll find a device that&amp;#039;s evolving into the dominant piece of technology for this century: the smartphone, Star Trek&amp;#039;s tricorder on steroids. Modern cars interface with smartphones for a world of entertainment and connectivity options. But smartphones are also changing so rapidly that cars have a terrible time keeping up. A medium-priced car only 5 years old probably won&amp;#039;t have Bluetooth connectivity for hands-free phone calls and audio streaming, a USB port for charging and data connections, an aux input for MP3 players, or an SD card reader and other features standard in center consoles these days. In another five years, current cars probably won&amp;#039;t interface with connectivity protocols or features of future devices. For those who like to keep their cars for more than a few years, this is a problem. But owners of older cars have options. There are plenty of aftermarket head units\u2014the boxes that radio hardware lives in\u2014that have advanced features and can connect to smartphones, and many of these units are just a few hundred dollars. A new head unit used to be the only way to get premium audio in nonpremium vehicles, but as society became more techy, automakers began differentiating their vehicles with quality stereos and high-tech electronics. In many modern vehicles, the audio system is deeply integrated into a larger infotainment operating system. Even so, cars take three to four years to develop, so their technology often lags behind the best phone features on the market. Aftermarket head-unit makers such as Kenwood and Pioneer don&amp;#039;t have to put their systems through the same rigorous testing procedures that carmakers do, so their development cycles are much faster, nearly as fast as those of phones. Since replacing a radio head unit is cheaper than replacing a car, this upgrade is a great option for keeping up with the times without spending a fortune. What and How to Buy If you want to upgrade your car stereo, better hope your vehicle subscribes to the DIN configuration. DIN stands for Deutsches Institut f\u00FCr Normung (German Institute for Standardization), which sets the standards for radio body sizes. A single\u2014DIN radio fits into a 2 x 7\u2014inch slot, while a double-DIN size is 4 x 7 inches. While this standard made sense for automakers in the past, they&amp;#039;ve been moving away from DIN-sized units and toward built-in nonstandard stereos integrated with other systems of the car (alarm, navigation, etc.).  All audio units operate similarly: 12-volt power comes in; circuitry and processors generate signals that drive screens and speakers. Mating a universal aftermarket radio to a model-specific speaker and power wiring can run the gamut from plug-and-play (easy) to running new wiring (hard). In the past, cutting into the original wiring and splicing in a new harness to fit the radio was the only way to make the upgrade. Fortunately, adapter kits can be ordered for just about every car now. Also check if an output converter is needed (a box that makes the new radio work with the factory speakers), as well as an antenna adapter or faceplate filler panels to make up for gaps that may be created. The one downside to an aftermarket radio is that many are, uh, aesthetically challenged. Finding one that combines tech upgrades and cleaner looks might take a bit of searching, and it won&amp;#039;t match your car&amp;#039;s interior perfectly. For around $200 a good-quality unit should come with a full-size USB port for charging your devices and Bluetooth connectivity for calls and media streaming. Double DIN units are bigger and have more features; some radios have foldout touchscreens and all kinds of goodies. Of course, your budget and needs will dictate your pick. Android or iPhone users should look for a head unit that can control the phone directly. We&amp;#039;re fans of both the Parrot Asteroid and the Kenwood KDC series, which is what we picked up for this install. Extract and Install &amp;amp;gt;  Getting the old radio box out sometimes means pulling trim pieces off first, so use trim-removal tools and be gentle. Spring latches hold the radio in place, and small slots or holes in the face of the radio provide access for a removal tool that may be needed for your specific car. Often a flattened piece of solid wire will do the trick, though. With the latches released, wriggle the radio out. You&amp;#039;ll need to detach the antenna coaxial cable and some quick-disconnect wiring before you can set the old box aside. Your car might be fitted with a standard metal mounting frame. If not, as was the case with our Audi A4, slide the kit frame into place and bend out a few of the metal tabs to hold the frame in place. If you have an appropriate adapter harness, plug the factory connectors into the adapter and plug the adapter into the radio. All DIN connectors look the same, but they may have different pinouts, so if you&amp;#039;re replacing a previously installed aftermarket radio, the wiring setup may not be an exact match. Before finishing the install, check the radio, make sure the speakers are working properly, and link and test any phones or players you may want to use. If a fuse blows, retrace your steps, since a wire is likely hooked up incorrectly. Once everything works, push the new radio body into the DIN slot until you hear the latches click on both sides, locking it in place. Install faceplate adapters and replace any trim you may have pulled off.  PS: The Hard Way If you can&amp;#039;t find an adapter, you&amp;#039;ll need to either splice into the factory harness or build an adapter. I prefer doing the latter to avoid chopping up the original wires. Fabricating an adapter harness from strand wire and spade connectors bridges the gap between connectors; it&amp;#039;s a cleaner method and lets you go back to stock much easier. The hard part is identifying which wire is which. Most are labeled, believe it or not, but a wiring diagram in a service manual can clear up any uncertainty. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/how-to/a8261/how-to-revamp-your-car-stereo-14522194/>