Hero’s Clever Trumpet Automaton: A 2,000-Year-Old Doorbell
Much of the technology we have today is inspired by some of the most fascinating ancient inventions in history. One of these inventions was Hero’s trumpet automaton, which is considered to be one of the earliest forms of the doorbell. Hero, an ancient Greek engineer and mathematician from the 1st century AD, came up with a number of inventions in his lifetime, including the simple steam engine and the cuckoo clock. One of the most fascinating, however, was the trumpet automaton.
The trumpet automaton was used to announce the arrival of someone to important buildings such as temples. But in an age where electricity was not yet used, how did this ancient doorbell even work? And why was it so important to the leaders of these important buildings?
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In addition to Hero’s trumpet automaton ‘doorbell’ and ‘automatic’ doors, prolific inventor Hero also created a simple steam engine (Archivist / Adobe Stock)
A Greeting and an Alarm
During the 1st century AD, there was no similar invention that would alert those in a building to the arrival of a guest. This ancient trumpet device was primarily used at temples throughout Alexandria, so visitors to the temple could be greeted and monitored. While it was originally a way to keep track of visitors to the temple, it was eventually used as a deterrent for thieves and other criminals. Since opening the door to the temple would produce a loud trumpet sound, entering without detection for mischievous purposes was no longer possible.
Although there is some record of these devices being used throughout Alexandria’s temples, it is not entirely clear if this invention took off outside of the temples and Alexandria. The invention was listed in Hero’s Pneumatica, a book describing his many inventions and ideas. While some of these inventions were implemented in real life, others were simply suggestions for future products that may or may not have ever been developed. So, it is unclear how successful or widespread the device actually was in the community. It is possible that if it were liked enough, it may have been used in other buildings, such as shops and restaurants.
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A model of Hero’s trumpet automaton, on display at the Thessaloniki Technology Museum (Gts-tg / CC BY SA 4.0)
Interestingly, it seems that Hero’s trumpet automaton was at one point combined with an additional invention of his. According to Hero’s Pneumatica, he once designed a device that could open doors using similar engineering methods. The door would be attached to a contraption that functioned using heated air and water. However, it would require human intervention to light a fire to get the contraption to work properly.
According to Hero’s description, a fire would be used to heat the air inside a vessel. This warm air would then increase pressure in a vessel containing water, which would displace that water into a bucket. Once enough water was in the bucket to weigh it down, it would fall and pull a rope attached to a pole, which would then rotate and open the door. On the other side of the device was a counterweight that kept the doors closed. Once the fire was put out, the pressure would decrease in the vessels and the process would be reversed, closing the doors for the evening.
Given the illustrations provided in his description, it is assumed that this device would have also been used in the local temples. The heated system would have simply held the doors open for visitors to come in and out with ease, while the trumpet system would have been used to announce the arrival of new guests.
In addition to Hero’s trumpet automaton, the Pneumatica also described an early automatic door system, which may have been combined with Hero’s trumpet automaton doorbell device. (Public Domain)
Old-School Engineering for Champions
The engineering behind the trumpet automaton is truly fascinating. Since electricity was not yet in use, Hero had to use hydraulics and air compression to get his ancient doorbell to work. Hero described the structure of this device in his Pneumatica.
First, a rope was tied to the temple door. The other end of this rope was then tied to a wooden lever, so the lever was pulled when the door is opened. Attached to this lever was a round vessel with an open bottom and a trumpet bell and mouthpiece attached to it, which produced sound once the system was properly assembled. The opening on the bottom of the vessel was filled with air but also exposed to a few inches of water.
When the door was closed, the vessel remained hovering over the water, as it was held up by the wooden lever. Once the door was opened, the lever pulled, lowering the vessel’s bottom into the water. This then pushed the air in the vessel upwards and through the trumpet pieces, producing a loud trumpet sound. Once the door closed, the vessel was lifted back up by the lever in preparation for the next guest.
A Quieter Modern Welcome
Doorbells today are quite different from the trumpet automaton. Instead of using hydraulics, today’s doorbells use electricity to produce a sound after pressing a button. Those without electric doorbells, such as small storefronts, may use a chime hanging from the door to make a sound when a customer enters.
Just as doorbells and chimes alert others to the arrival of a guest, the trumpet automaton functioned as the world’s oldest ‘doorbell.’ Without this device, guests to the local temples could enter quietly and without attention. With the implementation of this device, the arrival of guests became more obvious, decreasing the chances of crime within the temples. While the invention originally started as a greeting device, it eventually became a great security device too.
The next time you ring a doorbell, think of Hero’s ingenious invention, and be grateful you don’t have a trumpet blowing in your ear.
Top image: Hero’s trumpet automaton was a type of early doorbell, announcing the arrival of guests and dignitaries Source: Vibe Images / Adobe Stock
By Lex Leigh
Ancient Greece: Heron’s Trumpet Signal. History of Physics. (September 18, 2020). Available at: http://www.history-of-physics.com/2017/08/ancient-greece-herons-trumpet-signal_14.html
Combing, B. (2014, October 1). The First Automatic Doorbell in History? Strange History. Available at: https://www.strangehistory.net/2014/10/02/first-door-bell-history/
Renaissance Fun: The Machines behind the Scenes on JSTOR. JSTOR. (2021, February 24). Available at: https://www.jstor.org/stable/j.ctv18msqmt
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