Hey,

I just wanted to know if it was possible to make my horn beep when I lock my car (KH Xi, with original alarm and remotes)?

Cheers!

Sure, find active wire on central locking that engages when the button is pressed/key is turned and tap it into the horns active wire (will require a relay or something so as not to draw power on the locking circuit.

I suck when it comes to knowing what kind of circuit is needed for things but it's definitely doable, and fairly easily.