A candle clock is a special type of candle with markings that indicate the passage of time as it burns. It was used in the past to tell time indoors, especially during the night or on cloudy days. By sticking a heavy nail into the candle at a specific mark, it could also be turned into a timer.
When the wax around the nail melted, the nail would fall and make noise, serving as an alarm.
Before alarm clocks were invented, people used nails fixed on candles to wake up. They knew how to calculate the time it took for the candle to burn and placed the nail accordingly. As the candle melted, the falling nail would create noise and wake the person up.
The use of candle clocks can be traced back to ancient times, and the earliest reference to them comes from a Chinese poem written around AD 520. They were also used in Japan until the early 10th century.
