In France, sirens have been the principal tool designated to alert the population in the case of danger. However, their efficacity has not been objectively tested. Using a geographical information system, questionnaires, and surveys, we analyzed (1) the spatial distribution of the siren network in relation to the covered population, the hazards threatening different areas, and the actual number of disasters that have occurred in the past, (2) the political dilemma of activating sirens, and (3) the population's trust in sirens, as well as its understanding of expected behavior in the case of an emergency. Results show that, with a few exceptions, siren coverage in France is primarily determined by population density, not by the expected hazards or the cumulative number of past disasters. Sirens are also rarely used by the authorities. However, surveyed members of the population identify sirens as the most effective alert system over other alternatives such as cell-phone-based alerting tools. In a "mock" emergency most members of the public did not know how to respond in the case of an emergency, and even most of those who correctly identified the appropriate response prior to the exercise did not react upon later hearing the siren. To improve the effectiveness of the French siren network, we recommend (1) relocating sirens to optimize their efficiency, (2) complementing the sound of sirens with a clear and unified message, (3) reorganizing the competencies to activate siren alerts, and finally (4) improving public education on different alert tools and expected behavior during an emergency.