Fake kill switch to alarm?

I would like to install a kill switch. I would also like to install a fake kill switch thats easier to find thats goes off a certain amount of time even if they turn the switch off. Anyone with any ideas? I was thinking a glow plug relay that would set off a siren but when they turn the switch, it would cut off. I would like it to go off a set amount of time before it cuts off even if the switch is turned off. Ideas people? :banghead: