Random horn going off when parked.
 

Random thing started happening with my FR-S. (2013, 950 miles) After my commutes to and from work (about 20-25 minutes, mostly highway), when I park the car in the garage at work or home, after about 15 minutes or so, the horn goes off in between 6-8 times in quick succession. After that, never happens again. Factory Scion alarm on it. I'm wondering if I have a sensor somewhere that isn't quite placed right and as the car cools, it sets it off, like a light impact or something. Any ideas?

Get it checked out.

The FRS has electrical problems. Next will be your passenger sealt belt and windows.

I get that as well, and I also have the factory alarm installed. I'm pretty sure it's just the alarm sending off warnings due to slight vibrations/shaking. My alarm used to go off fully at the slightest vibrations in the road, so I had the sensitivity lowered, and now it's fine, just the occasional few horn sounds.

Here is an update with a test I did. Came home and started a stop watch, at almost 10 minutes exactly, horn goes off. Waited 10 minutes, went into the garage, started it for 30 seconds, turned it off and started the watch, at almost exactly 10 minutes, horn honk again. Going to test this again here shortly after the car has completely cooled down and see if it repeats. If it does, I think she's trying to tell me something.

this happened to my brz also... went to the dealer they told me they haven't had any cases of it. They told me if it comes back again, see them at the next service and see if other people had the same issue...

summary: they dont care