The present disclosure provides a sensor unit that includes a mounting portion fixed on one side of the sensor unit; an elastic member including a first end and a second end, the first end being disposed on the mounting portion; a transmission portion configured to transmit a detectable signal, the transmission portion disposed on the second end of the elastic member; a reception portion configured to receive a reflection of the detectable signal; and a controller that determines whether the reflected signal indicates an impact, motion, or impending impact.