The Hotun Detect Audible & Visual Alarm System for Hotun Tundish. The Hotun Detect HD-S1P is designed for Hotun dry trap tundishes, which safely discharge water from boilers or water heaters to an internal pipe without allowing odours back into the building. It helps save water and energy by not heating wasted water. This system is suitable for any application requiring an active warning light and can also help installers advertise regular maintenance to consumers. The alarm senses the presence of water and temperature in four stages and requires no specialist knowledge to fit. It is battery operated (batteries included).