[petar_prog]

Someone explained it properly in the reddit thread, it's the exhaust generating noise while driving in reverse (only happens in the morning when cold and at specific RPM, exhaust generates a specific frequency which vibrates the windows and triggers the alarm).

[alister]

> Someone explained it properly

That's a hypothesis, a very good hypothesis, but the Reddit thread and Hacker News offer many other reasonable-sounding hypotheses. I can't tell you the number of times I've tracked down a bug or other type of malfunction where I was 100% sure of the cause since my hypothesis made so much sense, but it turned out to be wrong. It was something else.

[_Nat_]

Alternative hypothesis, for the sake of example -

Someone's just really be into practical jokes. Possibly the neighbor whose alarm keeps going off, or possibly a third-party who found an easy way to trigger the alarm.

But, my first thought on this thing triggering when he backs up is a rear-view sensor that uses a projection to get data. Apparently the 2018 version of his car has radar sensors that go off when backing up (https://www.subaru.com/engineering/safety.html):

> Rear Cross-Traffic Alert uses radar sensors to help warn you of traffic approaching from the side as you are backing up, utilizing an audible warning and flashing visual indicators in your side mirrors and Rear-Vision Camera display

[DonHopkins]

I wonder if backing up would set off other people's radar detectors.

Reminds me of "Trolling for Taillights"!

http://www.cs.cmu.edu/~hgobioff/public/random_stuff/traffic

[jandrese]

Seems like the neighbors home security system should have a log of which sensor is tripped. Once you know that it should be pretty easy to figure out what is going on.