Multi-Frequency back-up alarms provides a solution to potential noise pollution created by conventional tonal back-up alarms in confined or densely populated work areas. Those Multi-Frequency alarms maintain a safe warning signal for those in the danger zone of backing vehicles while minimizing disturbance to work site neighbors. Multi-Frequency alarms operate by emitting sound at multiple frequencies attenuated above 4000Hz. In addition, the reverse mounted speaker design of the EA6100, EA9724 and EA9780, and the driver technology used in the EA7020, EA7070 and EA9070, models extends the life expectancy of the alarm, so much so, that a life of the vehicle warranty is offered.