Looking at the power consumption should be enough in most cases unless they generate their own electricity which should also be easy to figure out... from my home I can wirelessly read the power meters of about 30 of my neighbors (updated every 1 to 5 minutes) using a cheap rtl-sdr and a raspberry-pi (I probably could do better if I placed the antenna outside of my house or if I optimized the antenna for the frequency)

Stop dancing on the head of a pin!

Land value tax. No income tax. People who add no value get nothing.

Or a land value surtax which you don't have to pay if you are already paying income taxes or retired.

http://www.macleans.ca/economy/economicanalysis/a-roadmap-fo...

Then I can avoid the tax by using a timer device to switch the lights on and off

You can also shoplift and almost certainly get away with it.

Most people won't go through the trouble though.

You wouldn't pay a small power bill and buy a timer to save >$10000/yr?

Maybe it would work and maybe it wouldn't. And if they catch you, then they will multiply the fine.

What I'd do is just rent out the room, and not pay the fee.

You probably should use a somewhat random timer and include some heating and cooling too...but yeah it probably could be tricked fairly easily.