What is aux-in? 19 October 2016 by Gareth Evans What does an aux-in connection do? Find out whether you need it Parkers tells you all you need to know Enlarge 1 photos Main image caption What is an aux-in connection? An aux-in (or auxiliary-in) socket in your car is a 3.5mm jack into which you can plug anything that has a standard headphone connection. It sends sound to the multimedia system, enabling you to ‘stream’ music from a device through the car’s speakers. How does it work? Any device that features the correct 3.5mm socket can be connected to a car. You simply need an auxiliary cable with the same ‘headphone’ plug in each end to marry the two. It’s the simplest type of media connection, so can’t send commands along with the music. This means if you want to change track you’ll have to do that on the device itself, rather than being able to do this using the car’s controls like most other connections, including Bluetooth and USB. It’s impossible to use this sort of connection “handsfree”, in other words, thus you risk falling foul of ever-tightening laws regarding using handheld mobiles while driving. Furthermore, it won’t charge your device. Do I need it? That depends. If it’s your only option to transfer sound between your device and car then it’s a very useful addition. However, the lack of control and charging facility means many other types of connections can offer more functionality. Found on Many new cars as standard equipment or as an optional extra. Similar to USB, HDMI, Bluetooth, Android Auto, Apple CarPlay, auxiliary connection, headphone connection. Looking for more jargon-busting motoring meanings? Head over to our Parkers Car Glossary page and take a look at our other definitions. Advertisement What is an aux-in connection?