I don't have it but could get it if I wanted it.  Local coop has a bunch of them out.  My tanks are 1000 and 500 gal and I know they have a number of home heating fuel tanks on the system that are only around 250 gallons.  Size doesn't matter.

The way I understand it is it involves having a wireless monitor from the tank plugged into the phone system and it calls the coop every day to report the level of fuel.  We don't have a phone in the shop or barn, so the phone unit would have had to be in the house and the wife didn't want it in the house.  Pretty much end of story.

Only problem I've ever heard about was one gal had one on her fuel tank in the basement and her sex offender son was sure it was spying on him, so he removed it.  The coop refused to give her another unit and took the loss on the first one.   You get all kinds I guess.