For about a year I too have had the problem that is consistant among 04 and 05 impreza owners. I dont know if the problem exists in the 06 model. About a month ago I installed my new STI replica front strut bar and I had to remove the Chirp module that was in the way clamped to the strut tower.

Jumping arround before I move foreward, my friend has an o5 wrx jnust like i do but his is a later production, mine is novermber and his is january, I have noticed alot of differences, one that he has a chirp module, what I belive to be a chirp module, in front of the radiator. I have 2 one in front of the radiator and one clamped on to the strut tower.

Going back while installing my strut bar I though well my chirp hasnt been working for a while now so whats the use of relocating it...so I just removed it. After installing my strut braces, I cleaned everything up and closed my dors and locked my car, and what do you know it chirps again. After inspecting what had been going on I plugged back in the "faulty" chirp module and the chirp stoped. Every time i would remove the faulty one it would work again... After inspecting the faulty module I noticed it was full of water mineral deposits.

It seems to me that these chirp modules are very senstive to water and heat as my chirp seems to disappear everytime I wash my car or if my car sits in the heat for a while. One question why does my car come with 2 modules and the later production only come with one.

Sorry I dont have pics but I had been wanting top post ,my findings for quite some time. I will upload pics tomorrow to better assist on what im trying to explain..

http://i3.photobucket.com/albums/y73/txl146/IMG_0523.jpg image taken from another thread...

yeah I've already had mine replaced once under warranty.

that's just an additional horn that augments the alarm.... don't think it plays a part in the arm/disarm cycle

why do some cars have it and some dont then??

That is the security horn. It is part of the alarm option, so it will only be present if the car has the security upgrade to the factory keyless entry system. When the alarm is triggered that horn will sound.
On the 02-03, there was no separate "chirp" beeper, the vehicle horn was used as the confirmation chirp for arm/lock and disarm/unlock.
On the 04-up, a separate electronic beeper was added, mounted up by the radiator, to provide the chirp.

why do some cars have it and some dont then??

for the alarm optioned vehicles, it's addl security.... not too hard to duck under the lower radiator intake and snip the wires to the factory horns.... the horn up top by the shock tower isnt accessable til the hood's open.

my car has this and my friends doesnt our cars are identical both have keyless and alarm...

dont forget i have lo jack.

THat doesnt explain why mine had it and yours doesnt....maeby your just gay...

haha joto! im going to the movies after work. im going to watch that kacking movie. we going on friday right?? amado like pitos the tinto ones. i just wanted to add that.