Welcome to A2K. Sorry but your request is unclear. English seems not to be your first language. That is OK. I'll try to help where I can.
A speaker is what allows you to hear the audio. A mic is what you speak into to create sound waves for converting into an electrical signal for the computer to transmit.
More confusion on your term scanner? If you're talking about the copying device that converts a printed image into a file that's transmitted to the computer - then it's unclear as to why you'd need to hear it. There's no audio associated with this type of scanner. There's no mic or speaker associated with this device.
However, if you're talking about a combination device possibly? Then there's a camera combined with a microphone. If it's this sort of device, then it is within the software settings (application) of that device where you can adjust the sensitivity or volume associated with the mic.
One more possibility: are you talking about a radio scanner...of broadcast frequencies..like a police scanner?