Abstract: A spare tire pressure monitoring system includes a detection mechanism releasably connectable to the valve stem of a spare tire and includes a sensing device for measuring the actual air pressure contained in the spare tire, a selection mechanism for selecting an air pressure desired to be contained in the spare tire, and a transmitter unit for transmitting signals corresponding to the actual air pressure and the desired air pressure; a monitoring unit having a control mechanism, a receiving unit for receiving the signals from the transmitter unit, a display unit for displaying the desired air pressure, a discriminator mechanism for determining the difference between the desired air pressure and the actual air pressure, and an alerting mechanism that is activated when the difference between the desired air pressure and the actual air pressure varies from certain predetermined magnitudes; and an energy source.