I found a series of blog posts for a couple dozen emergency whistles.
bigpigblog.com/2014/05/05/whistlemania-i/
bigpigblog.com/2014/05/15/whistlemania-ii-the-iceman-cometh/
bigpigblog.com/2014/05/28/whistlemania-iii-slippery-when-wet/
bigpigblog.com/2014/06/13/whistlemania-iv-sound-off/
bigpigblog.com/2014/07/09/whistlemania-v-come-sail-away/

The top performers for the mini whistles (decibel loss with child vs adult blowing, detectable range over water with adult blowing, and distinctiveness of tone) were the ACME 660, the ACR, the Hammerhead, and the Fox40 mini. The ACME 636 had a big 10 dB drop when blown by a child instead of an adult, and the Fox40 micro/SOL rescue howler came in dead last with an 11 dB drop and a 1/2 mile range while most of the rest could reach out to 3/4 miles.

Because of this, I ordered the ACR to compare with the 636, and did an impromptu test using a smoke alarm as a reference. It was daylight savings time, so I was changing the smoke and CO alarm batteries anyway. I was wearing high fidelity ear plugs (Hearos) to protect my ears as is my habit when working with the alarms.
The 636 was slightly (objectively speaking) louder than the smoke alarm, and had its distinctive trill.
The ACR tone sounded almost exactly like a smoke alarm, but much louder.
The smoke alarm (Kiddie i9060) was rated at 85 dB at 10 ft, so 95-96 dB at 3 ft. I believe the rating to be accurate.

The ACR, because of its lower air requirements, and smoke alarm tone, has replaced 636 in my urban travel kit. The 636 went into my small gear drawer (whistles, knives, lights, pouches, and specialty batteries) for carry as the situation requires.