The chilling story behind the invention of the first baby monitor.

Today, baby monitors are a familiar fixture in the home of almost every young family. They allow parents to hear when their child wakes, and more modern devices include a camera, so a baby’s movements can be monitored when their mum and dad aren’t in the room.

This piece of technology, however, is less than a century old. And it was one, tragic story that led to its creation.

It was a Tuesday evening around 9.30pm in March, 1932 when Charles Lindbergh, a well-known American aviator from New Jersey, who had been the first person to fly solo across the Atlantic Ocean five years prior, heard a sound coming from his kitchen. He thought it sounded like the slats of a wooden crate snapping, but the noise wasn’t enough to alert him to leave his library and identify the source.

Roughly half an hour later, the family nurse, Betty Gow, went to check on Lindbergh’s son, Charles Jr, who was 20 months old. She discovered, however, that the baby’s cot was empty.

After checking that Charles Jr. was not with his mother, the nurse alerted Charles. Immediately, he went to his son’s room, and found a ransom note sitting by the window, and a broken ladder on the other side.

The ransom note contained multiple spelling and grammatical errors, and read as follows:

Dear Sir!
Have 50.000$ redy 25 000$ in
20$ bills 15000$ in 10$ bills and
10000$ in 5$ bills After 2–4 days
we will inform you were to deliver
the mony.

We warn you for making
anyding public or for notify the Police
The child is in gut care.
Indication for all letters are
Singnature [Symbol to right]
and 3 hohls.

The Hopewell police were contacted and a search of the premises was conducted immediately. In Charles Jr.'s bedroom, investigators identified muddy footprints, but there was no sign of blood or fingerprints.

Over the next few days, household employees were interviewed and the Lindbergh's made it clear that they were willing to negotiate with the kidnappers. Three days after Charles Jr.'s disappearance, a second ransom note was found, now demanding $70,000.

For the next month, a total of 12 ransom notes were delivered by the kidnappers, outlining a series of requests and claiming the crime had been planned for a year. In early April, $50,000 was exchanged for a thirteenth note containing Charles Jr.'s location, which stated the baby was on a boat called 'Nelly' near Martha's Vineyard in Massachusetts. An extensive search, however, found no sign of Charles Jr.

On May 12, 1932, the body of a baby boy was found just a short distance from the Lindbergh property. It was badly decomposed, and partly buried. The body was soon identified as that of Charles Jr., and an examination by the Coroner found he had died two months prior - likely on the night of the kidnapping. He was killed by a blow to the head.

By this stage, the Lindbergh kidnapping was a nation-wide news story, and the investigation into Charles Jr.'s murder attracted even more media attention. It wasn't until September, 1934, however, that there was a breakthrough.

Approximately $40,000 of the ransom money had been paid in gold certificates, making it identifiable when it was spent. In September, 1934, a number of gold certificates were discovered, and police began to track their location.

Ultimately, it was a petrol station attendant, suspicious of the $10 note he had received, who recorded the number plate of the man who had given it to him. This man, police found, was Bruno Hauptmann - a German immigrant.

When Hauptmann's home was searched, a large portion of the Lindbergh's ransom money was located. He maintained that he had been given the money by a friend, and had no connection to the crime.

Hauptmann was charged with both extortion and murder, and stood trial in January, 1935. While the prosecution's case wasn't particularly strong, and was based purely on circumstantial evidence, there was immense public pressure to convict. Perhaps the most damning evidence against Hauptmann was samples of his handwriting that matched the writing on the ransom notes left for the Lindbergh's.

In February, Hauptmann was found guilty and sentenced to death by electrocution. He died on the evening of April 3, 1936, and always maintained his inn

Over 80 years since the crime and ensuing trial, many believe Hauptmann wasn't guilty of the murder of Charles Jr. In fact, some are convinced it was Charles Lindbergh who orchestrated the kidnapping as a publicity stunt, and unforeseen circumstances saw it go horribly wrong.

Nonetheless, the high-profile nature of the case ensured it left behind a significant legacy. In the wake of Charles Jr.'s murder, kidnapping becoming a federal offence in the US, and the president of a company called Zenith, Eugene McDonald, was inspired to improvise with radio equipment, speakers and microphones to record noises from his daughter's room. He hoped the device would prevent further tragedies like the one that had befallen Charles Jr.

In 1937, the Radio Nurse - which closely resembles modern baby monitors - was made commercially available.