Hey folks, long time board member, but have been very quiet since the old boards shut down. Figured it might be time to come back with a call for help on a non-gun related issue, lol.
Anyway, to all you car electronics experts out there, I just bought my son a used 2015 mustang and found what appears to be an aftermarket security ad-on, but I can’t figure out exactly what it is. Pics are attached. It is mounted under the dash at the driver’s right knee. It acts almost like a proximity sensor, it starts blinking a green LED when someone walks by and the engine is not running. It also has a button which I think is an ignition cutoff or valet mode. But not really sure. Any and all help is always greatly appreciated.
t’s the valet/programming button (with integrated status LEDs) for an aftermarket dealer-installed car alarm/security system, very likely a KARR system.
KARR (and similar systems from Directed/Viper, Compustar, Avital, etc.) was a common dealer-added option on new cars around the 2015 era. Dealers installed them for lot security/inventory tracking and to upsell “premium security” to buyers. The button is almost always tucked under the dash (often near the steering column, fuse box area, or kick panel—just like in your photo). The green oval face with the four white dots is the status LED indicator pod (the dots are the LEDs that light up or flash in patterns to show armed/disarmed/valet status, or during programming).
Why your 2015 Mustang works fine without it
The alarm is almost certainly in valet mode (or the previous owner bypassed/disabled the active alarm features while leaving the wiring and button in place). In valet mode, the system disables the siren, door triggers, and any starter-interrupt functions so the car operates normally. That’s why you’ve had no issues—the system isn’t actively protecting or interfering with anything.
What the button actually does
Press/hold it (usually with the key on or in a specific sequence) to toggle valet mode on or off. This is the standard way to temporarily disable the alarm for service, valet parking, car washes, etc.
It’s also used for programming the remotes or entering diagnostic mode on the alarm module.
The green LEDs give visual feedback (flashing patterns, solid on, etc.).
You can see nearly identical buttons in dozens of “mystery under-dash button” threads on Tacoma, Ridgeline, Accord, Passport, and other forums—every single one turns out to be a KARR (or equivalent) valet switch.
Should you remove it?
You can safely ignore it or tape over the LEDs if they ever annoy you. If you want it gone, don’t just cut the wires—some of these systems have an immobilizer component that can cause starting issues if improperly removed. The proper way is to put the system fully into valet/disabled mode first (usually by holding the button with the key on until the LEDs go solid), then disconnect the module. A car audio/alarm shop or your dealer can do it quickly and cleanly if you’re not comfortable.
That’s the whole story—classic used-car leftover from a dealer alarm. Nothing to worry about, and now you know what the “mystery button” is! If you want to test it yourself, try the valet sequence (ignition on → press/hold the button for a few seconds) and watch the green LEDs to confirm. Let me know if anything changes or if you want the exact disable steps for your specific setup.
Yeah, I saw that too, and it might well be a valet switch, but i’m not 100% sure though. There is only 1 LED on the narrow face, and those 4 circles on what appears to be the button are dimples, not LEDs. Also, google AI told me it is possibly just a proximately sensor for an aftermarket alarm system which could have been removed but the sensor left, and what looks like a green button might just be a sensor hump. I honestly don’t know which AI to believe, and I am weary of pressing any unknown buttons. I posted the same question to the mustang forum to see if it was something specific to the mustangs. Worst case I will have to take it to an alarm shop, but I really don’t want to spend money just to figure out what it might be.
There’s an old saying. “If it ain’t broke, don’t fix it”. I’d put a multi-meter to it and see if it is drawing current. Might just be an orphaned switch.
Yeah, I just looked up KARR system and found a few posts, including a video of the system screwing with the cars ignition. It’s not an issue now but it is definitely active. My son drives this car to school every day and I don’t want him to end up with problems while driving to or from school. Even if it’s not causing problems now I don’t want to risk it failing in the future.
Any good reputable stereo/alarm shops in the manalapan area?
Depending on how confident you are with car wiring you could remove the under dash panel and take a look. Maybe the splices are minimal and easy to figure out.
I used to be very comfortable when I was younger. Replaced the entire head unit and added front and rear cameras to my 2015 Camaro. But these days, I would just rather pay someone else to do it.
From what I read in that reddit thread, these tended to be installed using obvious T-taps, so if you don’t mind getting your head up in the fuse block area you might find them all.
getting under the console was always a back breaker.