I was wondering about this myself,
I know in the U.K they sometimes use some kind of heat seeing cameras on helicopters to pick up the heat from grow lights.
Ive read about in the U.S the power companies will rat you out to the cops if they see something suspicious in your power usage times.
Id love to know what kind of tactics they use over here to actually catch people,I know at least one person who posts here has been caught,but i dont
think they said how.