The first commercial hearing aid was the Akoulallion, invented in 1899. Initially the battery packs used to power hearing aids were large and carried in separate boxes or strapped to the leg where they were less obtrusive. In 1934, however, the first vacuum-tubed hearing aid was developed. Hearing aids with the battery incorporated into the device itself did not appear until 1944. This ‘Ardente’ battery-operated hearing aid can be dated to the early 1930s.