@markjgabb "..cut back all unneccicary steps and really locked down what was going on.." was indeed the idea.
What I went on to explain is than you are reporting the state of D3 which goes HIGH/LOW/HIGH via the button, not the light. The critical difference between @skywatch and your install is movement detection maintains a value, your button does not.
If you create a variable before the loop, say boolean lightswitch=false; (presuming that the light is ON when you program it) this variable will be changed and reported to Domoticz in the loop.
Top of the loop you toggle the "lightswitch" value, first time it will switch false to true, report in the "lightswitch" value then go to sleep.
Bottom of the loop your " sleep(digitalPinToInterrupt(DIGITAL_INPUT_SENSOR), CHANGE, SLEEP_TIME); should trigger on a LOW, as this is the momentary state of D3 ONLY when the button is pressed.
Your next button press activates the loop, toggles "lightswitch", reports and goes back to sleep, at least two years on a pair of AA cells.
Were it I doing this there would be a mains powered indicator on the switch plate which cuts out when the light is on, A- To find the switch in the dark, B-To provide an indicator which can be used to verify the actual state of the light to ensure it stays in sync (Murphy's Law).
I don't see the point of using heartbeat as it is not a security device, and only fire the battery reading mosfet every X loops.
