At the pre-opening bell, frontline index S&P BSE Sensex opened in red with a loss of 194.52 points or 0.24%. On the sectoral front, metals slipped by 0.40%, power plunged 0.35% and auto dropped by 0.15%. Meanwhile, Rolex Rings Ltd, Suven Pharmaceuticals Ltd and Sudarshan Chemical Industries Ltd emerged as the top gainers of BSE in the pre-opening session today.