Assuming a low level of noise in the house, I’ve always been able to hear the tornado sirens in the various houses in which I’ve lived in Springfield. I can even hear the siren tests at my desk at work on the first Tuesday of each month. This was true of old sirens as well.
Short of putting a siren in everyone’s front yard I’m not sure what more can be done. I mean, have you ever been right next to one of the sirens when it has gone off? I have. If it were any louder, it would probably kill you. If the weather looks bad, turn on your radio, TV or get on the internet (my preference) for severe weather statements. Or you can go out and buy weather radios that automatically come on when severe weather threatens. There’s no need for louder sirens.