If your car triple honks when powering down the car, it's not something that you're doing wrong. My 2017 does it, it's reproducible and this is due to a software and hardware problem.Earlier today I ran through the drive-thru at Dunkin and then parked for a moment to get situated before taking off again. My fresh coffee was cold, so I shut down the car to go inside and get it replaced.
The instant I turned off the car, it startled me a bit with the dreaded "triple honk"...
There were no messages on the DIC or anything. I was able to lock and then unlock the doors with the button on the handle, and it started back up fine, without any messages about the remote or anything. Random anomaly, or was it trying to subtly tell me something?
Edit: I should note that all the doors were closed when I shut it off, as usual.
The software issue is due to the triple honk when powering down the car. There's no logical reason for the triple honk when powering down the car and it's not one of the conditions listed in the user manual. The hardware issue is related to the detection for the keyfob because it's not reliable and while this is my opinion, it should detect the keyfob anywhere in the car. Explanations like "One of the computers got confused" should be discarded and only lead to further confusion when trying to understand the problem.
To reproduce the triple honk, put the keyfob on the right rear of the front passenger seat. Try powering down the car listen for the triple honk. If it doesn't do it, move the keyfob to random areas in the car and keep trying the process over until you hear the triple honk. The triple honk will occur eventually.
Its been said that you cannot lock your keyfob in the car but that's not true. You can (I've done it) because the keyfob sensor cannot detect the keyfob in many places. Another example of the keyfob sensor not working well is when my keys are in my bag, which I normally put on the front seat. When a passenger gets in the front seat, the bag goes in the back seat. If I open and close my door, a triple honk occurs. This shouldn't occur because the keyfob is still in the car.
I agree that the triple honk is annoying and unnecessary. When I get time, this function will be removed with a hardware modification.