The Talkboy was Kevin McCallister's portable audiocassette player that can record and change sounds, including people speaking, and play music. Kevin also used the talkboy to change the pitch, telling the operator in a deep voice, "Howdy-do, this is Peter McCallister, the father. I would like a room with a extra large bed, a TV, and one of those refrigerators you have to open with a key" and "Credit card? You got it."
Kevin listens to his talkboy inside the aeroplane in the second film, causing him to miss the fact he caught the wrong flight.
Some of the other things he records, include an advertisement for the Plaza Hotel, his Uncle Frank singing in the shower, and yelling at him, and the Wet Bandits telling him about their plan to rob Duncan's Toy Chest.