The earliest type of hearing aid is in fact still used in modern times. Whenever you see a person cup their hand behind their ear, you are seeing the first method of hearing assistance in action. Born out of necessity, the earliest tools used to aid hearing came about in the early 17th century. They were the long trumpets that sailors held to their ears to hear the calls of other sailors on distant vessels. Smaller versions of these ear trumpets were used in the later seventeenth century to help people with hearing loss; they were of the same type – a cone or trumpet inserted into the ear and then pointed at the sound. Another form of 17th century hearing aid was called the Metal Ear, and that's exactly what it was – a pair outsized ears fashioned out of metal and worn over the wearer's own ears. In the 19th century smaller forms of these acoustic horns were marketed as Auricles or Cornets. These devices were portable, but cumbersome. The end collecting the sounds was generally placed in a strategic orientation on a table or carried in a purse. A flexible tube then carried the sound to the ear.
Electric hearing aids came out in 1898 on the heels of the invention of the telephone. They were not too dissimilar from the ear trumpets that preceded them. However they did noticeably expand the range of frequencies that could be amplified. A hearing aid using vacuum tubes was patented in 1921. The vacuum tube – based hearing aids wasn't commercialized and sold to the public until 1934 because of its large size and bulk. Because of the vacuum tubes, it needed an amplifier, a microphone, an ear receiver, and two batteries that, despite their size, only lasted for a day. After that, there were no significant improvements in hearing aids until 1947, when the transistor was invented. It took a full five years – until 1952 – for transistors to find their way into hearing aids. The engineering challenge that had to be solved was keeping the transistors dry since they are very sensitive to moisture. The invention of the integrated circuit in 1958 led to their first widespread use in hearing aids, a trend that continued until the 1970s.
When microprocessors and digital circuitry became available, they too were used in hearing aids, creating features impossible before that time, such as multi-band technology, noise and feedback management, and directional microphones. The new technology had its downside too. Since each hearing aid was hand-crafted, prices were very high and wait times were long.
The first commercially successful digital hearing aid was created in 1987, and used a body-worn processor connected via a wire to a receiver in the ear. The first all-digital hearing aid was introduced in 1996, and advances in technology have now made them the standard, possessing features undreamed-of by the 17th-century ladies with their ear trumpets.