Answer: microphone

AnswerCrossword Clue
MICROPHONESound investment?
MICROPHONEPart of a walkie-talkie.
MICROPHONEEmile Berliner's 1877 good idea
MICROPHONEIt's used in some addresses
microphoneAn instrument for converting sound waves into electrical energy variations, which may then be amplified, transmitted, or recorded
microphonean instrument whereby sound waves are caused to generate or modulate an electric current usually for the purpose of transmitting or recording sound (as speech or music)