Hooking up aftermarket horn

I'm considering installing this horn in my tacoma:

http://www.griotsgarage.com/product/compact+italian+air+horns.do?sortby=ourPicks

I used to have that same horn in my old VW GTi. I've gotten rid of the car and no longer have this horn, but it is definitely very loud. I had to wire in a relay because this thing draws 18 amps and I didn't want to fry the wires. I'm thinking I will have to do the same in my Tacoma.

My question is:

Does the factory Tacoma have 2 horns? 1 that is meant for the alarm and one that is separate for the actually horn button? That was how my old car was setup.

The reason I ask is because I don't want to hit "lock" on my key and have the crazy loud after market horn go off... I only want it to go off when I press the the horn button on my steering wheel.

edit: Now that I think about it, i think my truck "beeps" when i hit lock and unlock so maybe I don't have to worry about this issue! All I have to do is hook up a 4 prong relay to my existing horn and wire up the new horn this way.... inputs/comments appreciated!

 

I believe the arm/disarm confirmation is a beep, not the horn as you already indicated. However, if the alarm does go off I believe it uses the horn for the alarm. I would consider this an advantage as far as having a really loud horn. It should be easy enough to confirm this, hit the panic button on your remote to verify...