I don't believe they have to get a search warrant. I just think the police sometimes, in hotbed marijuana growing areas, just use this technology to seek out large grow ops. They don't go to a judge for permission to use modern technology and hover over an area. That's like saying they need a search warrant to patrol a certain zip code.

If the police have sufficient evidence, ie lots of infra red coming out of a shed in the middle of nowhere, THEN will the judge issue a search warrant to search the property.

But no judge in the world would issue a search warrant over a few infrared lights that are stationed in a suburban home, you have absolutely nothing to worry about.