 These small devices are installed on the property gas meter (usually between the utility company's metered installation and the structure piping) and are designed to instantly stop the natural gas supply in order to protect the structure if a gas leak or line break occurs during an earthquake.Fires or explosions due to gas line breaks can be more damaging than the actual earthquake itself.Gas supply companies recommend that the gas supply be cut off immediately if there is a smell of gas after an earthquake; if nobody is in place to do this, an unattended earthquake valve will instantly cut off the gas.