attachInterrupt(0,wakeUpFunction, LOW); // use interrupt 0 (pin 2) and run 
                                          // function wakeUpFunction when pin 2 gets LOW

#include "Arduino.h"                 // required for eclipse IDE
#include <PinChangeInterrupt.h>
 
#define USVActive   0                // Pin5 - Input
#define BUTTON_DOWN 2                // Pin7 - Input
 
// flags to indicate if interrupt has been detected
volatile boolean flagIntUSV = false; 
volatile boolean flagIntBUT = false;

pinMode(BUTTON_DOWN, INPUT_PULLUP); // ISR-PIN reading Button
pinMode(USVActive, INPUT);          // ISR-Pin reading digital value
 
attachPcInterrupt(BUTTON_DOWN, ButtonInterrupt ,FALLING ); // assign ISR: ButtonInterrupt ()
attachPcInterrupt(USVActive, USVInterrupt ,FALLING ); // assign ISR: USVInterrupt ()

void loop() {
 if (flagIntUSV) USVHandler(); // if ISR has set ISR-Flag: call dedicated function to do something
 if (flagIntBUT) BUTHandler();
 sleepNow();                   // sleep function called here; the program will go to sleep here and wait for interrupt
}

void sleepNow() // here we put the arduino to sleep
{
 set_sleep_mode(SLEEP_MODE_PWR_DOWN); // the most power savings sleep mode is set here
 
 sleep_enable(); // enables the sleep bit in the mcucr register
 // so sleep is possible. just a safety pin
 
 attachPcInterrupt(BUTTON_DOWN, ButtonInterrupt ,FALLING );
 attachPcInterrupt(USVActive, USVInterrupt ,FALLING ); // CHANGE
 sleep_mode(); // here the device is actually put to sleep!!
 // THE PROGRAM CONTINUES FROM HERE AFTER WAKING UP
 
 sleep_disable(); // first thing after waking from sleep:
 
}

void ButtonInterrupt(void) {
 volatile long lastMicros = micros() - prevIntBUT;
 prevIntBUT = micros();
 if (lastMicros >10000) { // debounce 10ms
    flagIntBUT=true;
 }
}

void BUTHandler(void) {
 flagIntBUT=false;
 detachPcInterrupt(BUTTON_DOWN);
 
 // do something
 Serial.print("-------- Button pressed ");
 attachPcInterrupt(BUTTON_DOWN, ButtonInterrupt ,FALLING );
}