I purchased an investment property with a main house and a detached garage with a finished apartment over it. What is the best way to monitor utilities for the garage apartment? The property is on one account currently. Utilities will be charged for longer term rentals only (i.e. not VRBO).
I use sub meters for my commercial property - for electrical. Some of these are wifi connected, others require a manual read. I use the Leviton meters, but some people like EmonDemon. Leviton are cheaper. You have to bill the tenant for their electrical use.
If the garage apartment has it's own subpanel, the sub meter is easy to install. If it's circuits are intermingled with the main home, then you're either out of luck, or you'll hire an electrician to put them into a sub panel.
Gas is tougher to sub meter. Supposedly there are "gas sub meters" and "BTU meters" but I haven't used them. Honestly, you might consider getting the utility to install another meter that serves just the garage apartment. Also, if you have the sub panel for electric, it might be more straightforward to get the utility to install another meter for the garage.