A typical smoke alarm makes a very high pitched noise.
This piercing sound is ideal for people with normal hearing.
But for people with high frequency hearing loss
(especially many seniors)
this sound is beyond their hearing range
which means: they may hear only a faint beeping
even at close range, or they may hear nothing at all.
A popular Dear Abby article makes note of this deficiency in typical alarms.
See the original article here.
The Loudenlow makes a lower frequency tone which is much easier
for many people to hear. The pitch is around Middle C (250Hz) and carries throughout a house
Hear it now