The Multi-Frequency back-up alarm provides a solution to potential noise pollution created by back-up alarms in confined or densely populated work areas by maintaining a safe warning signal for those in the danger zone of backing vehicles while minimizing disturbance to work site neighbors. The Multi-Frequency alarm operates by emitting sound at multiple frequencies attenuated above 4000Hz so that the sound is perceived to dissipate more quickly than a conventional pure-tone alarm.