Estoy haciendo una App para operaciones matemáticas y le incorporé un cronómetro con alarma. Cuando la ejecuto y la dejo en segundo plano o mi celular bloqueado, a veces desbloqueo para ver como va el tiempo transcurrido pero mi cronometro esta en ceros, le establecí que en 15 minutos debe sonar la alarma, pero a veces tampoco suena. Cómo puedo corregir ese error?
Are you using an extension?
Change your thinking about the timer, to a deadline stored in TinyDB.
That will live across shutdowns and restarts of your app.
Use a Clock Timer to periodically check if you have reached the deadline (Clock1.SystemTime)
By the way, AI2 can't run in the background (though there are battery-draining work-arounds)
the alarm doesn't sound if the app is in the background and the timer is at zero
see also App Inventor Tutorials and Examples: Countdown | Pura Vida Apps
the workaround is to keep the screen on...
the tools extension offers a method for that App Inventor Extensions: Tools | Pura Vida Apps
Taifun
Trying to push the limits! Snippets, Tutorials and Extensions from Pura Vida Apps by 
Taifun.