Seismometers, which detect and measure earthquakes, have been used for many years. Chang Heng invented the earliest seismograph during the Han Dynasty in 132 A.D. He called his invention a "dragon jar". It had a pendulum that moved easily, so that any minor earthquake would cause the pendulum to hit the gold sides of the jar, warning the people. Because the gold used in the early seismographs was so expensive, only the rich could afford them.
Did you know that ancient folklore told people that when megapod birds quickly left their nests, and seasnakes crawled onto the sand, that the volcano would soon erupt?