This thing works just perfectly for this old house with no neutral wire. I'm using it to control a bathroom vent fan. Here are some things to know:1) You do need to connect this exactly as the instructions say even when you have two black wires that aren't labeled properly as to which one is hot and which one leads to the load (light, fan, etc.)2) The earth ground is required for operation and not just for safety! if you don't see a green wire, look for a naked copper wire which is probably connected to the wall box. You can attach the green wire either directly to the naked wire or screw the green wire to the wall box if the naked wire is screwed to it.3) if you have two black wires, and don't know which one leads to the load, just try to guess based on where the wires are coming into the box. If you know the path through the walls to the load device then that will help. If you guess wrong, the switch won't work properly. In this case just shut off the circuit break and swap the black wires. After that it should work.4) When you restore power, the switch might start up in the "on" state and your load (fan, light) might be running. Just wait a minute or less and it will shut off as soon as the capacitor in the switch charges up. Then wait a few more minutes and the switch should be working as expected.I think the switch probably uses a design like US Patent US5903139A. This charges a capacitor, not a battery, so should have a decently long lifetime.If you do have a neutral wire in your house (2 phase AC power) like most modern houses, then you're probably better off with a design that makes use of the neutral wire and the 2nd electrical phase to power itself. That will avoid the start up delay.