Being curious about everything I just had to test this spare module I had.
The module is made to accept an input from a piezoelectric knock sensor, but I hooked it up to a signal generator instead in order to test it.
It turned out to be completely unresponsive to continous signals, so I needed to "tap" the signal to the input (blue wire) in order to simulate "pings".
The output (black wire) is at 10V nominal (w/ pink/black wire supplied with 12V) and drops down low (with varying pulse widths) when activated.
A stronger input gave a broader pulse width, but I just used a DVM instead of an oscilloscope this time to get ballpark readings.

The minimum input needed was 80mV (rms) and was centered around 6.1kHz.
At 250mV (+10dB) it responded from 2.8kHz to 13.2kHz.
At 800mV (+20dB) it responded from 1.2kHz to 32.3kHz.

I don't claim absolute accuracy of these measurements (but it's close enough), and these ESC modules doesn't seem to be "rocket science" anyway.
Also, in real use the sensors characteristics is added to this.
I'm just posting it here for reference in case someone is curious about it or could use the info for something practical.