When do I need to press the button on the Diamond device?
And is it supposed to be just light up when I press the button but off once I not pressing it?
I am not a "Diamond" user but I have an AQ SUB-3 subwoofer cable, which has the same device "DBS".
The device works automatically. The function of button and light is only for checking the battery condition. If you pressed the button and the light is dim, then it is the time for you to change the battery. That's all.