The birth of the detective: Six surprising tools and techniques used for solving crimes in the 19th century

If you thought 19th-century innovations were limited to lightbulbs and steam engines, then think again. From invisible writing on egg shells to secret listening devices, the 1800s saw the birth of a range of technological advances that helped Britain and her allies in World War Two and inspired James Bond and the modern-day spy. The acclaimed author C.A. Asbrey investigates.

C.A. Asbrey

The 19th century was a time of great innovation and invention. In The Innocents Mysteries, I identify a number of ways in which criminals and detectives raced to beat one another. Some of the techniques were used right through to active service in WW2. Here’s five of the most surprising.

1. Wiretapping

Crippen is often cited as the first murderer caught by telegraph, but in 1845 John Tawell was apprehended fleeing from Slough. He had poisoned his mistress with prussic acid to avoid paying child support. Before the advent of Morse Code, the system used at that time didn’t have a ‘Q’. Once the police worked out that the message told them that the man ‘dressed as a kwaker’, was in fact, a ‘Quaker’, they apprehended the man dressed in the full-length black coat who had been travelling in the exact carriage described to them. The case helped the telegraph system to spread. By 1870 it was possible for London to communicate with Bombay in minutes.

However, people have been tapping into wires for as long as they have been used for communication. In the telegraph system it was stupidly simple. It was basically a huge circuit, so could be accessed by attaching a wire and listening in to clicks which passed along it. Wiretapping was routinely used by both sides in the American Civil War, criminals used it to listen to plans to transport valuables, and businesses used it to keep up with rivals. It didn’t stop there either. It was also used to spy on gangs during the prohibition era, and even on Civil Rights leaders in the 1960s.        

2. Ciphers and codes

These are as old as writing. Any message could be intercepted. Pigeons could be shot down, messengers captured, and letters stolen. There are many different kinds, but in the 19th century two main kinds were popular. Playfair Cipher is created by generating a random short phrase, and then constructing a 5 by 5 grid of letters. That grid is the required to decode the message. As the alphabet had 26 letters and the code 25, ‘I’ and ‘J’ are interchangeable.

The other is One Time Pad. That is a symmetric encryption system using keys that are changed with every single message. The code takes its name from the fact that the keys were originally written on pads of paper and the name One Time Pad stuck. It requires both the sender and recipient to have the same key. It is best for short messages ads the more the code is repeated the more elements there are which can be used to crack it. 

3. Invisible inks/hidden messages

Invisible inks are the stuff of legend. They are either organic or synthetic. Many things have been used from plant sap, lemon juice, milk, onion juice, urine and even sperm. They are developed either by a chemical or by a process like heat, which acts on the ink at a different rate to the paper or fabric the writing was on. Acids, alkalis, heat, or light were all the reagents used

One very old method, which dates from, at least, Elizabethan times, was still in use during WW2. A mixture of alum and vinegar was used to write a message on a boiled egg, which is not visible on the shell once dry. These eggs could then be transported amongst raw eggs. Once peeled the writing was visible in the stained alum inside the egg. You can easily tell a boiled egg from a raw one by spinning it on a hard surface.

4. Spy cameras

Think that these were impossible in the days of long exposures? Think again. The invention of Gelatine dry plates in the late 1870s made shorter exposures practical for the first time. In 2007 a spy camera hidden in a watch sold for £21,600. We have no record of the oldest version in existence, but we can be sure that this example, made by Lancaster & Co in Birmingham, was not the first. Small hand-held cameras were in use from the 1850s, and then they started to be concealed in hats, clothing and bags. By the 1880s fully commercial versions were being openly demonstrated and sold as novelties. The one sold in 2007 was made for a woman.

5. Listening devices

Joseph Toynbee invented the artificial eardrum as a hearing aid in 1852. It didn’t take long before more devious minds saw another use for the vulcanised rubber disc which amplified sound through a rod. They used them for listening through walls or from a nearby table. The Victorians tendency to try to make disability less visible also meant that they came hidden in hats, elaborate hairdos, and even tiaras.

6. Gadget canes

We’ve all seen the swords hidden inside canes, but the Victorians loved hiding all kinds of things in them. Of course there were telescopes, listening devices, keys to ciphers, maps made of silk which could occupy a tiny space and even bottles for poisons. Cane guns were invented very early in the 1800s. Speaking of poisons, there were even poisoned cigarettes which would kill when eaten to evade interrogation or torture.

C. A. Asbrey is a former police officer whose Innocents Mystery series of historical fiction novels are written from a female perspective and highlight the forgotten role of pioneering women detectives.  Her novels are based on true events and are historically accurate. Her new book, Innocent Bystander (Prairie Rose Publications) is out now on Amazon UK  priced £4.55 as an eBook and £11.40 in paperback. Further information about C. A. Asbrey and her books can be found at

By C.A. Asbrey


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