What I do from time to time is to use my whole house power monitor to see what is happening. It is made by Efergy and shows KW's to 3 decimal points. i can easily see the 400 watt block heater turn on. I have found block heaters I have used to be among the most reliable stuff I own.
I understand and have experience with the high tech. In my working life I had 120 buildings spread out over a wide area controlled by digital control systems all interconnected by the internet. Keeping those systems operating so that the readings they sent out were actually correct and equipment, claimed by the system to be operating, actually was in operation, required a full time crew of about 10 people supplemented by companies like Johnson Controls' experts.
In my retired personal life I did not want to continue with the high tech solutions.
Everyone's situations are different and their solutions will reflect their lifestyle and skills.
Dave