They asked the parents of thirty children to set off the smoke alarms in their properties at random hours of the night. ‘Eighty per cent of these children did not wake up, even though some of them had the alarm in their bedroom.’ The variable frequency detectors designed to address the problem of heavily sleeping children seldom worked. Some of the most effective alarms are reported to be the ones that allowed the mother to record a message herself: ‘So she says, “Get up!” and children respond to the pitch and frequency of her voice.’
