I use the AudioMoth with a external microphone underwater and to monitor marine mammal.
Did you put it in salt water? It is ok for the microphone?
Can you share some more results?
Did you protect the piezo hole or it gets in direct contact with water?
How did it perform?
About 2 meters!
What depth are you deploying it at?
That’s great. They were £25 each last time I checked but now seem to be down to £1. They are also supposed to be much more uniform in their response - less variability across manufacture.