Water-level change warning device and coal mine gas extraction system

The utility model discloses a water-level change warning device and a coal mine gas extraction system. The warning device comprises a floating ball, a power supply, a warning motion switch and an alarm, wherein the warning motion switch and the alarm are connected with the power supply, and the warning motion switch comprises a movable connecting rod and a contact. The floating ball is arranged on the water surface of a water pool to be detected and connected with the movable connecting rod of the warning motion switch. The contact of the warning motion switch, the power supply and the alarm form a series connection return circuit. The water-level change warning device is simple in structure, low in cost and strong in reliability, can monitor water-level change in real time and generate alarm signals automatically, reduces labor intensity of workers patrolling the water-level change and improves security coefficient of water-level monitoring.