floors of fear
^ Nightingale Floor via zen-garden
In order to detect human presence inside a house, and as a protection measure against ninja stealth walking, Nightingale Floors (Uguisu-Bari 鴬張り) were invented in Japan around the 17th century. By means of a simple timber and nails construction detail, the weight of a person walking on the floor boards was automatically translated into squeaking sounds, alerting anyone in the adjacent sleeping quarters. The rubbing of the nails up and down with metal clips is what produced a bird-like sounding friction. This alarm made soundless moves visible to the inhabitants of the house, which could prevent domestic crime at the time: a potential murderer could not remain unseen at night.
Samurais were even said to make a more sophisticated usage of the Nightingale Floors in their own houses. A system through which they could control the device to the point of making specific tunes out of their walking. A new language to communicate with the others in the house about whether they needed to worry or not about their presence.
^ Nightingale Floor via wikipedia
^ Nightingale Floor in Nijo Castle, Japan. Construction detail via biglobe