UL 217 and listings
Something to be aware of: It is apparently possible for a product to be listed to an earlier edition of the UL/ANSI 217 standard that is not the current one. UL won’t do that of course. Listing to an earlier edition could be a way of circumventing some of the more recent performance requirements, such as the 7-day battery back-up requirement in a smoke alarm or accessory, and requirements for the 520Hz mixed-frequency signal harmonics (see a previous post about the 520 Hz signal). So it turns out to be possible for a manufacturer to claim a listing to UL 217 for a smoke alarm accessory that might not comply with current UL 217 requirements. It occurs to me that this may be the case with other products and standards. If you are considering a purchase, it may be prudent to verify the standards edition that a piece of equipment is listed to.
The Lifetone HLAC series of smoke alarm accessories of course is listed by UL to the current editions of UL 217, UL 464, UL 1971, and cUL S531 for use in the US and Canada, and listed as a low frequency sounder. We’re kind of proud of that as you might guess.
Product listings by UL can be verified by means of the UL Online Certifications Directory. You can enter the manufacturer code above a UL mark (like S24639) or a company name (like Lifetone Technology). The directory will return the current listing cards for the products made by that company.