To provide a monitoring system which is improved in versatility.

The monitoring system 1 is comprised of a house sensor device 2, an automobile sensor device 3, and a single monitor device 4. The automobile sensor device 3 includes a microcomputer 31 and a transmitting means (a transmitting circuit 32 and a transmitting antenna 33). The microcomputer 31 acquires information indicating that an automobile is used in a mode equivalent to a state where a warning should be issued. Only when the information indicating that the automobile is used in the mode equivalent to the state where the warning should be issued, is acquired by the microcomputer 31, the transmitting means transmits a warning request signal indicating that the automobile is in the state where the warning should be issued. The monitor device 4 includes a receiving means (a receiving antenna 41 and a receiving circuit 42), and a buzzer 45. The receiving means receives the warning request signal transmitted from the automobile sensor device 3, and when the warning request signal is received by the receiving means, the buzzer 45 issues the warning.