Self-contained power supply relay system. Efficient switching power supply providing optimized current output based on number of sensors. 1/2 in. snap-in nipple attaches to standard electrical enclosures through 1/2 in. knock outs providing easy installation. UL 2043 plenum rated for cost-effective installation. LED indicates status of relay or if there is a low-voltage overcurrent. Constructed with environmentally friendly materials and is RoHS-compliant.