This paper focuses on experimental findings on the waking effectiveness of different auditory signals in \udchildren, deep sleeping young adults, older adults, the hard of hearing and the alcohol impaired. Wherever \udpossible, data is graphically presented in terms of the percentage sleeping through different sounds at 75 \uddBA. It includes previously unpublished data comparing the waking effectiveness of various signals in \udyoung adults who were either sober or moderately impaired with alcohol. A summary of the evidence \udconcerning the best and worst signal shows that the 520 Hz square wave signal is at least 4 to 12 times \udmore effective than the current high pitched signal in the populations tested. Research supporting lower \udfrequency signals and mixed frequency signals as being the best alarms for people when awake is also \uddiscussed. It is argued that the 520 Hz square wave signal, which has been tested now in six different \udexperimental studies, has a sufficient evidence base to warrant the recommendation for its widespread \udintroduction as a new smoke alarm signal for the whole population. Not improving the alarm signal is \udlikely to result in fatalities and injuries that may have been avoidable.
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