How to check if handler has callback

There is no way to check if it has a particula runnable. You can call

handler_Alerts.removeCallbacks(r_Alerts); 

to remove any instance of r_Alerts inside the Handler queue, or

handler_Alerts.removeCallbacks(null);

to remove all the runnable in its queue

is that possible to check has the postDelayed() was called or not?

One quick fix, in method assign some boolean variable to true and then just perform checking.