makeshift alarm

I have a 1997 chevy silverado with keyless entry and I installed a relay that when I lock the doors I have a neg.input to the relay the ground for the horn the neg. door triger and 12 volt power to the relay I want the horn to honk when the doors are opened and stay honking till the dome light goes out. I can do this except for when i get out before I can set my alarm I have to wait till the dome light goes out first if I dont the hornwill honk till the light goes out any suggestions how I can make this work?

partsexpress.com sells a keychain transmitter and 12 volt reciever that you could wire a channel to so that you could turn the alarm on by remote after the dome light goes out. you could also rig your current setup so that the alarm is only turned on by pressing the lock button on your remote, but you would need to isolate it from the rest of the system with diodes so that the alarm did not set itself every time you hit the lock button from inside the vehicle. you would have to tap into the existing keyless system between the reciever and the relays for your keyless, and if you wanted it to turn off the next time that you hit the remote to unlock the vehicle, check out the schematic that the 12 volt has for the radio that stays on until your dome light goes on and just hook it up so that after you arm your alarm, it stays on until the unlock relay is powered. this would take a little bit of design, but could definately work. let me know through 12 volt messenger if you want help designing it.