No search warrant is needed, sometimes. Went thru this is AZ. City code has alot to do with things. In Mesa AZ the code enforcer (yes, it is a real job) was the one that enforced stuff like unregistered cars sitting on your property. As long as the car had current tags they generally did not bother you. But I observed the code enforcer walk up my neighbors driveway and lift the car cover to verify it had current tags on it. I asked him what he was doing and the disagreement escalated until the cops showed up. Found out later that if the vehicle is in sight of the general public (in another words your front yard) that it has to be operational and current on the tags. If it is in the backyard, does not matter. I agree, it is bs about being told what you can and can't do on your own property. Where we live now is an un-incoropated county. No problems with vehicles sitting on your property. At times I wish there was. There are several properties with 15-20 cars sitting on them. This kind of stuff does not do much for property values.