I actually bought this relay not expecting to use the LOW trigger option. Actually I just wanted a simple 5V relay that I wanted to control via mosfet. It turns out that the output of the trigger contacts gives out only 2.5 volts, which is not enough to work with. I connected this relay to a 5V supply as directed, connected one of my 120V wires to my 24V supply, set the jumper low and connected it to a pin that supplies 2.5V, and it works great, allowing me to turn my 3d printer on and off using the on screen buttons, automatically on failed and finished prints, from my phone, from any computer, from anywhere. ports.