I've got a friend in Tokyo, Japan who has a 370z. He pm’d me to say that it's possible to reset the horn to ‘two-tone’ (he’s done it himself) – apparently a few owners have done it on his forum (sounds like a crap idea to me, but each to his own). There are also rumours of other ‘tweaks ‘ that have been hidden in the system for people to find.
Apparently you sit in the car (with your intelligent key), press the brake pedal 12 times within 10 seconds, then press the horn 3 times within 5 seconds and finally depress the brake pedal 12 more times within 10 seconds and the tone of your horn will change from a single note to a two-tone. Repeat it and the tone becomes ‘normal’ again. Apparently, timing is critical. I’d try it myself, but we don’t get our 370z’s in the UK until June/July – you yankies/japs have all the luck!!!
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EDIT - Now that the truth is out there, I ought to warn any new visitors to this thread that it was an April Fools Joke - It got a few people who admitted trying it ......and maybe a few others who have kept quiet since they stopped annoying the neighbours with their mindless horn tooting! 