In the last few years, many fatal accidents have been reported that involved backup maneuvers on construction sites, even when the vehicles had functional sound alarms complying with current regulations. Various factors can explain the ineffectiveness of these sound devices in alerting nearby workers, and hence the interest in considering independent mechanisms of hearing perception in designing safer systems. The author analyzed current personnel detection techniques that could complement or replace these devices, and determined the safety criteria that are applicable to vehicles used on construction sites. The conclusions could apply to other mobile equipment, mainly in mines and the agricultural environment.