When it comes to matters of safety, the Japanese don't mess around. Hence the Door Opening Warning Light, which helps you avoid accidents when opening your front door. Take the two parts of the Door Opening Warning Light, put batteries in (sold separately) and fix them on your door, near the knob (they have strong magnets so no tools are required). Switch it on and close the door. Every time someone comes near it (from 4m/13 ft on), the device's panels will light up, warning you that you shouldn't rush. The display is shown in either icons, Japanese letters or by plain light (you can select your preference).
The Door Opening Warning Light features: