Thanks for your answer.
The coupling of the oscilloscope is in DC, and the wave output should always be positive(offset DC), and a range of 9V or more, however, is 3,6V peak to peak and AC.
The output wave of zaper without connecting to the wristbands is the following:
When connected to the wristbands square wave disappears and turns into a train of pulses of 1V amplitude (as if the zaper neither could deliver current output).
The zaper is totally new and do not know if this is their normal operation.
Thanks again and greetings