Arduino (Counter as a Dead man Switch)

bool pressureIsStillIncreasing()
{
   bool goingUp = true;
   static int currPress;
   static int prevPress = 0;

   currPress = readCurrentPressure();
   if(currPress <= prevPress)
      goingUp = false;

   prevPress = currPress;

   return goingUp;
}

Write the readCurrentPressure() function to get the pressure from the sensor. Call this function once every second, half-second, week, whatever. If it returns true, leave the compressor running. Otherwise, turn it off, run in circles, scream and shout.