In case of sudden and extreme life-threatening situation, the most efficient system fulfils the requirement of mobile phone emergency alerting information services. But how much information and what type of content must be used in a textual message, and how adapt this alert to a large audience and diversified contexts? This paper proposes to address this challenge, 1) by presenting results obtained in France during simulated "alerting days", with sampling revealing the perception and understanding of SMS and CB by a non-specialized audience (161 respondents), and 2) by comparing findings obtained in different contexts (students and teaching staff in a university, crisis managers and stakeholders in an industrial context, citizens working near high-risky areas). Even if reactions to an alert are individual, similar patterns emerge, suggesting that standardized and non-random needs exist.