For centuries, Japan has taken pride in the talents of its craftsmen, carpenters and woodworkers included. Because of that, you might be surprised to find that some Japanese castles have extremely creaky wooden floors that screech and groan with each step.

How could such slipshod construction have been considered acceptable for some of the most powerful figures in Japanese history? The answer is that the sounds weren’t just tolerated, but desired, as the noise-producing floors functioned as Japan’s earliest automated intruder alarm.

The specially constructed floors were called uguisubari. Literally translating as “bush warbler guard watch,” uguisubari are more commonly referred to in English-language texts as nightingale floors.

In installing nightingale floors, planks of wood are placed atop a framework of supporting beams, securely enough that they won’t dislodge, but still loosely enough that there’s a little bit of play when they’re stepped on. As the boards are pressed down by the feet of someone walking on them, their clamps rub against nails attached to the beams, creating a shrill chirping noise.

▼ The place where the uguisubari magic happens.

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▼ Nightingale floors in action

As you can see/hear in the videos above, equipping a hallway with nightingale floors means that with every step someone takes, he announces his presence. This makes it incredibly difficult to move around stealthily, and thus nightingale floors were used as a countermeasure against spies, thieves, and assassins. By accounting for the size of the noise and the direction it was coming from, they could even be used to help pinpoint the interloper’s position.

Not just anyone could afford nightingale floors, but you can find them in historical seats of power. Kyoto’s Nijo Castle, built as a residence for the shogun during visits to Kyoto, is probably the nightingale floor location best-known to international travelers, but it’s not the only place to see this clever and classic home security system.

▼ Nijo Castle

▼ Higashi Honganji Temple, also in Kyoto

Of course, all of this raises one important question. If your security needs are high enough that you decide to put in nightingale floors, odds are you also have guards keeping an eye on your castle. So how do you tell if those chirping footsteps you’re hearing are coming from a trusted sentry or enemy ninja?

The solution is, like the floors themselves, elegantly simple. In order to tell friend from foe, the lord of the castle or captain of the guards would designate a set rhythm for allies to adhere to when walking on the nightingale floors. If they heard their “nightingales” singing at a different speed, they knew they had an uninvited guest, and that it was time to sound the alarm.

Basically, going on patrol was like a high stakes game of PaRappa the Rapper.

Source: Kaigai no Bankoku Hannoki
Insert image: Rohm