A streamer recorded the warning signal live on her cellphone just before the big earthquake. Japan has an effective earthquake warning system (EEW), which sends warnings to residents' cellphones or other devices before an earthquake arrives. EEW works with rapid detection sensors located around the country that monitor seismic activity. When sensors detect an earthquake, the system quickly analyzes the data and, if an earthquake wave is expected in a certain area, sends a warning through telecasts, radios and mobile phones. These warnings can be made seconds or even minutes before an earthquake strikes, which can provide valuable time to protect against potential hazards. Japan is actively investing in technology and infrastructure that could improve the ability to predict and respond to natural disasters such as earthquakes.