The House Is Not Clean by Chun-Fu Chen from taiwan

Harmful substances in the air are similar to the ghosts. We can’t clearly see them but they may impair our health seriously.
The dirty air enters the gap between transparent case and the outer filter. The bigger dusts are blocked at the outer filter and then the air passes through the activated carbon filter and go out from the rear outlet.
After period of time, the dust will accumulate and show a ghost-face image in order to insinuate users to clean the filter.
The ordinary air purifier can’t exactly show when we should clean the filter. However, “The House Is Not Clean” air purifier indicates the filter’s status with an intuitional and interesting way.