The phrase "aux in" is not correct or usable in written English.
It appears to be an incomplete or unclear expression, lacking context for proper usage.
Example: "The aux in my car is not working properly."
Alternatives: "auxiliary input" or "aux connection".
— Dual AUX IN jacks – Connect up to two additional audio players via front-facing 3.5mm jacks.
Power and volume controls are integrated and an AUX in jack is incorporated for hooking in your mp3 player.
The system connects to your var via a cigarette lighter power port and the Aux in jack of your stereo or via Bluetooth.
— Connect additional devices – The AUX IN jack and RCA adapter let you connect additional devices like your TV, game console, MP3, DVD and CD player at the same time your computer is connected.
The company has announced version 2 of its Chromecast product, along with a new Chromecast Audio, which turns any speaker with an AUX in into an Internet-connected device.
Collins said that the need for this device came out of the fact that everyone he talked to has some sort of speaker in their house, be it one on a nightstand, surround sound speakers hooked up to the TV or any speaker with an AUX in.
It supports aux-in devices via a mini-jack and also includes an FM tuner.
There is also an aux-in 3.5 mm jack for connecting pretty much anything.
You can mess with the privacy screens, front passenger seat position, XM channels, and Aux-in music.
It also has an Aux-In and the audio quality is pretty good for a standard dock.
Plus, the designer folk streamlined the look a bit and added a thoughtful aux-in jack for the iPod haters.
