Author Welles Wilder developed the Parabolic SAR. This indicator is always in the market (whenever a position is closed, an opposing position is taken). The Parabolic SAR indicator is most often used to set trailing price stops.
BUY{ SET PS = PSAR(0.2,0.02); SET MA = EMA(PS,21); SET MA2 = SMA(CLOSE,50); CROSSOVER(MA,PS) AND CLOSE < MA2;} LONGEXIT{ SET PS = PSAR(0.2,0.02); SET MA = EMA(PS,21); SET MA2 = SMA(CLOSE,50); CROSSOVER(PS,MA) AND CLOSE > MA2;}