Its not uncommon for older people ,,exspecially the elderly,, to lose the ability to hear high pitch sounds,,,exspecially smoke detectors,,i know alot of elderly family memebers and friends, that have this problem,,,bass sounds they can hear,,or may be a little hard of hearing ,,but its not uncommon as we get older not to be able to hear high pitch sounds,,personally,i would think it would be the other way around,,but its not,,i would still seek the advice from your dr,,,good luck,,bobber ,,,,,,,,,,,plus its dangerous to them and you when driving or walking thru a populous place,,and not able to hear a smoke detector,,,they do make devices to flash lights in your house when your smoke detector goes off,,,and or change the sound,,,good luck