Digging up a super old thread to help others out that may have been thinking about this stuff like I was...
Anyway, I wanted the beep, I also wanted the powered windows without the key in the ignition... I figured I'd try both at once...
I followed this thread for the windows (which work a treat):
viewtopic.php?f=13&t=18971In addition;
I bought a cheap waterproof siren 12/24v from Jaycar (LA-8901) and wired it into the positive door lock pulse (red wire with two grey spots). Gives a sharp beep when the doors are locked.
I mounted it it under the hood (rear passenger side) and it's loud enough to hear inside my house, but not agressively so.
I only did it for locking, as unlocking didn't concern me. I guess wiring in a couple of diodes and splicing the lock/unlock pulse wires together could easily achieve that (I may be wrong, feel free to let me know, I'm just thinking on the fly).
Anyway, just thought I'd finally give something back as this site has been a wealth of knowledge and is always my go to for anything Hilux related.