A directional back-up alarm deployed in a vehicle moving in an open space, in accordance with one embodiment of the present invention includes, in part, a first ultrasonic generator adapted to generate a first ultrasound signal; a second ultrasonic generator adapted to generate a second ultrasound signal; an audible sound generator adapted to generate an audible signal; a modulator adapted to modulate the first ultrasonic signal with the audible signal to generate a modulated signal; and a summing circuit adapted to receive and sum the modulated signal with the second ultrasonic signal to generate a combined signal. The combined signal is transmitted with a transmit antenna. The transmit antenna may include a Piezoelectric or silicon device.