A door bell and a switch would do. Or do you need it to be automatic, in which case buy a smoke alarm they are cheap enough
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Please don't trust your safety to a home made replacement of something that is readily available.. If you intend to use this to wake you so you can exit a burning building on time, then trying to make your own is on par with online medical advice; just don't do it. I mean, would you jump out of a plane with a home made parachute? Or drive in a car with home made airbags?