ITEM NAME:4-Channel 12V Relay Module with Optocoupler H/L Level Triger for Arduino #gib Store Home Promotion Hot Item Add to Fav.S1~S4:They are option switch for relay 1~4; 3. It is low level triger if COM pin connect to LOW pin; It is high level triger if COM connect to High. Power indicator light (green), relay status indicator light (red);.