apart from reading meters, what methods do electriccompanies use to monitor households electricity consumption

Answer 1

Meters can be read automatically from the office of the supplier or read manually every month.
Many times usage may be estimated. When that happens, the homeowner may feel it is too high, and the estimate may be.
It will always correct itself by a manual reading.

One should be aware that if one is stealing electricty, by hooking up directly to a power pole, (Dangerous without a transformer to cut down voltage), the power company will know that electricity is being consumed, without a meter.
Had a neighbor once who was caught doing this. Happenend to be an electrician.

Same holds true for a phone being used illegally. The power used is monitored from each line, and is known if a user does not have an account.

The electric power supplier even knows if usage is lower or higher than normal and may/will investigate the reason.
Some of those reasons are times when a customer adds an appliance or other high usage item to their home.
Sometimes they discover a faulty meter, recording less or more that actual usage.

Answer 2

kilowatts spent per month i dunno sorry you are going to have to wait