Transmission device for transmitting information about tire condition and tire condition monitoring system

A tire condition monitoring system comprising:

• a transmission device including:
• a sensor configured to detect, as tire information, a condition of gas filled in a tire cavity area surrounded with a tire and a rim;
• a transmitter configured to wirelessly transmits the detected tire information;
• and
• a housing which houses the sensor and the transmitter, the housing including a protruding portion protruding in a protruding direction from a surface of the housing, the protruding portion including a top portion defining an opening portion of an air vent connecting an inner space of the housing and the tire cavity area, the opening portion having an area of 0.4 mm2 or smaller, a height of the protruding portion being 1 mm or greater, and an area of a contact portion between the top portion and a contact plane that is in contact with the top portion and perpendicular to a protruding direction of the protruding portion is not larger than 30% of the area of the opening portion;
• a receiving device configured to receive the tire information transmitted from the transmitter;
• and
• a monitoring section configured to determine whether a tire anomaly exists based on the tire information and provide a determination result.