In a country with high seismic activity, reliable early warning systems are not a luxury but a necessity. The Alerta Sísmica México - SASSLA app, developed by Diego Ramirez, positions itself as a direct, mobile-based extension of the Mexican Seismic Alert System (SASMEX). It serves a vital function: providing those precious seconds of advance notice before strong tremors arrive, which can be the difference between safety and peril. The app operates primarily within the coverage areas of the official sensor network, including Mexico City and states like Oaxaca, Guerrero, and Morelos. Core functionality is deliberately focused. The app delivers official seismic alerts categorized by intensity—Preventive and Public—with a distinctive alarm sound and push notification. A live status indicator shows whether the alert system is active, in testing, or offline. For situational awareness, it includes a built-in seismograph viewer showing real-time ground motion from official stations and provides access to recent alert histories and details. The interface is utilitarian, prioritizing speed and clarity over decorative elements, which aligns with its emergency purpose. In real-world usage, the app’s performance hinges on smartphone settings and network reliability. Users must ensure notifications are enabled at the system level and that background app refresh is active for the alert to sound reliably, especially if the phone is idle. The distinct siren-like alarm is designed to be unmistakable, even in noisy environments. Practical scenarios involve users placing their phone in a consistent location at night or keeping it nearby during the day, treating the app as a dedicated alarm system. Its utility is greatest for those within the sensor network's reach; outside these zones, its effectiveness is limited. While the app store shows a high rating, specific user reviews highlight its life-saving potential. Feedback often praises the app's reliability and the critical few seconds of warning it provides, allowing people to evacuate buildings or take cover. Some reports note that during periods of high seismic activity, multiple or redundant alerts for the same event can occur, which is a minor annoyance compared to the benefit. A common suggestion from users is the desire for more granular location customization and detailed, post-alert information about the earthquake's epicenter and magnitude directly within the notification. Overall, the SASSLA app executes its primary function with effectiveness. Its strengths are its direct tap into the official alert network, a clear and urgent alert interface, and reliable performance within its operational zone. Limitations include its geographic dependency on the SASMEX infrastructure and the need for users to correctly configure their devices. It is not a global seismic monitor but a specialized tool for a specific, serious need. For those living in or visiting seismically active regions of Mexico, installing and properly configuring this app is a straightforward and highly recommended safety measure.