need a discreet sounding chirp siren

Yes, but you still need to control the duration of the pulse, and when it actually pulses.  You can't use a door lock actuator output because they are too long.  You need a dedicated controller.

You could possibly use an alarm siren output, but you would need to put a delay on the actual siren so that if the siren output is on for longer then ~0.5 seconds the siren kicks in and starts doing its thing.

I don't have an aftermarket alarm on my car, so I had to do the whole controller.  I also wanted my parking lights to flash, so I used every wire on the thing!

Looks very clean -- good show!  I haven't seen Molex or their competitors available to the general public.  Although I think of DigiKey for electronic components, connecters didn't occur to me!  I just today picked up a couple 1/8" mini-phone panel jacks and cable plugs and I expect my "project box" to arrive late next week :).  I'm using the wire left over from the keyless entry install.  I can get away with the mini-plugs because it's just two wires in and two wires out, but it isn't my preference for wiring a car.

I installed the "peeper" under the hood today -- there was one open spot on an actuator shelf adjacent the HVAC relay box at the far left of the firewall.  A single tiewrap secured it.  Routed the wiring through the fender like oem -- used quick disconnects for the actual connection to the piezo, but then taped and tiewraped them.  Can't finish it properly until the cabinet arrives, but it's working fine -- just need to turn down the loudness a tad.

Sounds like you went just a tad fancier than mine, but it also sounds like you didn't already have the keyless entry (I finished installing a standard box a little over a week ago.)  If the keyless entry controller thinks it's cool to flash the parking lights, that's good enough for me (the peeper will fire off too :)!) 

I used my OEM keyless system.  For some reason it flashes twice when you lock and not at all when you unlock.

I fixed it, though!

That does sound a little unusual!  My 1990 Eclipse didn't have keyless entry (they weren't big then), but it did have a factory security system.  So after I recently  picked up a Scion, I decided I liked keyless entry and wanted the Eclipse to have it too (on the other hand, the Scion DIDN'T have a security system, so I installed the factory accessory.)  That led to the Keyless Entry controller, remote lift-gate release, and then the "peeper" :)!  I'd still like to have remote lock security enable, and I'll probably be tinkering with that next!

By the way - thanks for the source info.  I've been looking them over and am impressed!  I see this Hammond box would have housed my oneshot nicely :)!  http://www.hammondmfg.com/dwg2XXFL.htm  Hopefully I have enough leftover wire for the remote-lock-security-enable project, otherwise, I may have to order some.

Did you etch your own PC board?  I'm using an old CSC Proto Board for breadboarding and even older perfboard for point to point building.  Does the job, but point to point wiring to DIP sockets can be a little hairy :).  Almost all bits and pieces come from a box of miscellany I accumulated over past years of playing with electronics, but I occasionally have to break down and purchase something :)!