MAGNETIC SENSOR

I have bought on banggood inductive detector (blue one) used between 6v and 30vdc. I have made a First test with a 5v power supply, i couldn't make beep my multimeter. I then try with 12v with different materials steel,copper and aluminium it works well but not so on copper. I will perhaps use it on my CNC for end stop

Brown wire is the +, Blue wire is 0v, Black wire is the output of sensor. I have connected my multmiter with black and blue wires.
i measure less than 100 ohms between black and blue wire during metal detection.