My car honks if you press the lock button twice, so you can verify that the car is locked if you're not close enough to see the lights flash. That's a nice feature.

You could wire the horn to the power locking mechanism ... or better yet to the remote receiver so that it only honks when you use the remote to lock the car. You'd have to get a service manual and discover the location of these things, though. It's probably in the underhood computer, not the ECU but the other unit that controls things like the windows and doors. It's probably near the fusebox. I know that's where mine is. I think it's called the MCP but I could very well be wrong. My memory is not good when it comes to 3 letter initials that I've only dealt with once or twice.