Abstract: An automatic earthquake gas shut-off system (11) is provided in two selected versions. The first version of the gas shut-off system (11) includes a spring pendulum (17), a first electronic movement sensor (21), an electrical control relay system (23), an electrical motor (25), and a housing (27). A several improvements to the first version may be made. These improvements may include one or more of the following. The use of a reset switch (61), a combination of a first bevel gear (37) and a second bevel gear (39), a combination of a second electronic movement sensor (53) and a third electronic movement sensor (55), a timer (65), a key (41), a rechargeable battery (67), and an activation switch (63). The second version of the gas shut-off system (11) includes, in addition to the elements of the first version, a pendulum damper (19) which may adjust the receptive frequency of the spring pendulum (17).