The Hearing Aid is one of the major characters from The Brave Little Toaster Goes to Mars.
He is a hearing aid who once belonged to a theoretical physicist named Albert Einstein a fact of which he is very proud. After he moved away, the Hearing Aid was left behind in a junk drawer in the kitchen.
One night, the Hearing Aid is heard talking to someone from space who sent him a telecommunication. He was invited to be beamed up to Mars for some unknown reason. However, Toaster and his fellow appliances become suspicious and intervene. In the commotion, Robbie (the Little Master) enters the kitchen and gets abducted instead.
The appliances restrain the Hearing Aid and discover that Robbie was sent to Mars, according to the Hearing Aid's readout on the Calculator. The Hearing Aid explains that he was supposed to get transported to Mars. He then assists Toaster and his companions on their mission to rescue Robbie.
When they arrive on Mars, the Hearing Aid is eventually reunited with his long-lost twin brother, who was the former Supreme Commander.
After rescuing Robbie, the Hearing Aid returns to Earth with everyone else, including his brother and Tinselina.