umm i have read that marijuana plants give off a slightly different signature that can be detected by a trained eye.. i have watched doc's about the dea raiding/finding fields in cali etc. this only works outdoors though because they need to be in plain view. i couldn't tell a big dif from the doc that i was watching but when the dea guy pointed the marijuana patches out you could see the dif.. for anything checking a home/warehouse for a grow they look at the heat sig, in which case your grow room(s) would show a ton of heat from the lights but as far as the infa red saying what you are growing indoors you can't. as far as anyone would know, you could just have a hot room, an indoor garden of tomatoes etc..