Waking up async the Arduino while it is sleeping periodically
My aim was to attach multiple interrupts to my Arduino but my problem was that I didn´t know if when the board changed to sleep mode using LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF) then it could be awake using another interrupt instead of the timer.

The void loop() method must sleep the board every 8 seconds if no button is pressed. Aside there is a method that is called when a button is pressed, that´s because in the void setup () I´ve attached an interrupt using PCintPort::attachInterrupt(PIN_NUMBER, METHOD_TO_CALL,MODE);



OP (PinaGamer) posted this answer inside the question, hence the community wiki answer.