The most effective alarm to wake a sleeping person with mild to moderately severe hearing loss is one that sounds, according to Waking Effectiveness of Alarms for Adults who are Hard of Hearing, a Fire Protection Research Foundation study released this month.

Several auditory signals and a variety of alternative alarms that employ methods other than sound, such as bed shakers, pillow shakers and strobe lights were studied for their effectiveness in alerting hard-of-hearing individuals of an emergency when they were asleep. Results showed that the standard audible emergency evacuation signal (a repeating pattern of three tones and a pause) with a lower pitch tone (520Hz square wave) awakened 92% of the hard-of-hearing participants when used at or below the code-minimum sound level of 75dB for 30 seconds. The same device awakened all of the participants when raised to 95dB (the typical sound level produced by smoke alarms). It was also noted that participants that awoke to signals were most likely do so within the first 10 seconds of the signal being on. The lower pitch tone was found to be significantly more effective than the higher pitch tone (typically 3,150Hz) commonly used in smoke alarms and other alerting appliances.

“It makes sense that people at higher risk of not waking up to a smoke alarm, like those hard of hearing, might seek alternative devices that they feel are more likely to alert them in an emergency situation,” said Kathleen Almand, executive director of the Fire Protection Research Foundation. “Finding that an auditory signal at a low pitch is best for alerting even those mild to moderately hard of hearing will certainly prompt further investigation in this area and ultimately lead to better protection for this high risk group.”

Based on the study, the overall single best option for alerting people with mild to moderately severe hearing loss are low-frequency square-wave auditory signaling devices, which surpass bed shakers, pillow shakers and strobe lights when presented alone.

“Interestingly, this is the latest in a number of studies focused on high risk groups that found low pitch alarms to be most effective for waking, an area that merits further examination,” said Almand.

Bed shaker and pillow shaker devices presented alone were successful in awaking 80-83% of the hard of hearing participants at the intensity level as purchased. Strobe lights alone were not effective in waking this population with only 27% of participants waking to a strobe light intensity above the lowest level permitted by code for sleeping areas.

The study includes several recommendations for further investigations based on its findings.