A tire monitor device for a vehicle has a first antenna and a second antenna, a sensor unit attached to each of a front left tire, a front right tire, a back left tire, and a back right tire, and a determining unit. A control wheel is mounted for rotation about an axis at an end of one of the limbs, and has a single peripheral groove that extends around such axis. A reference signal reception controller receives the reference signal and compares the reference signals to a predetermined filtering condition table.