Replace Wall Light Switch With Touch Sensor
Introduce a natural line to the switch too, use the 110/220 VAC transformed to 5VDC, then power the control circuit. not user friendly, but reliable.
#3. induced current from hot line to power the control circuit. most user friendly. but there is absolutely technical skill behind this.
Most such designs have an enormous problem of blinking of light. To kill the blinking, they also supply an “adapter”