Earthquakes generate two kinds of waves, moving through the earth's crust. The non-destructive, higher velocity primary waves can be detected by seismographs up to 60 seconds before the destructive secondary waves arrive at the same spot. Primary waves can, therefore, be an early indicator if the incoming earthquake will be potentially destructive or not. This allows warning people in advance. "Terra" has two modes, which differ through sound and light design. In case of an incoming non-destructive earthquake, a calming sound supported by a slowly pulsating light, advises the user to stay calm and helps to avoid panic. In the event of an incoming, potentially destructive earthquake, "terra" emits a strong alarming sound and an intrusive pulsating red light, letting the user know to take immediate action and seek shelter.