What does the stock alarm sound like when it goes off? Does the horn honk, or is there an actual siren?

Also, what does it take to set the alarm off?

It's the horn. Also, if you click "lock" twice on your remote the horn honks to confirm. The only thing that sets it off is someone opening the door with the alarm set. You can get an upgrade to a "shock sensor" which I think will sound the alarm for broken window and maybe if the car moves. Save your money and get some after market alarm. For one thing, you won't have the annoying confirmation car honk; rather have something quieter.

Originally posted by 8_wannabe
The only thing that sets it off is someone opening the door with the alarm set.Actually, it also protects the trunk and hood, and will even sound if someone manually unlocks either door with a slim-jim or reaches in through an open window and unlocks it from the inside.