Configured with positive-opening design of normally closed contacts, per IEC 60947-5-1 standards, SI Series monitors position of guards, gates, covers, and other movable machine fixtures and tooling. Units provide reliable monitoring regardless of environmental conditions and withstand any attempt to override switch and defeat system. Available with plastic or die-cast aluminum housing, switches offer multiple actuating systems, including plunger, roller, spindle-mount lever, and 2 lever styles.