It's also interesting that they might not have got a warrant to look at his garden for a month. They weren't looking for any particular behaviour - just something that would allow them to barge into his house and discover evidence of drug-related wrong-doing. If they had spotted (say) public drunkenness, they might also have argued that his house be searched. Putting up a camera to spot 'any tiny thing that the person does wrong' would seem to be very flimsy warrant-wise (I would hope).