A Divechime is a hand held underwater Buddy-to-Buddy Signaling Device.
You can get your Dive Buddy’s attention from over 100 feet away.
Divechimes are used by shaking them. Dive instructors are using them all over the world with no complaints. I guarantee them for as long as I live.
Just tell me one has failed (leaked) and I will send you another one, you don’t even have to return the failed one.