Governor Brown's hesitation to sign off on laws that restrict police action beyond constitutional limits seemed to motivate his decision to veto AB 1327. His veto message can be found here. From the veto message:
There are undoubtedly circumstances where a warrant is appropriate. The bill's exceptions, however, appear to be too narrow and could impose requirements beyond what is required by either the 4th Amendment or the privacy provisions in the California Constitution.
I agree that the law went beyond the restrictions required by the Fourth Amendment. But that is because Fourth Amendment restrictions on government drones are extremely limited, as I explain at length in this post. Under long-established case law, the government may use drones to conduct surveillance on people whether they are near their homes or driving in public without raising any Fourth Amendment concerns.
Privacy advocates are therefore understandably disappointed with Governor Brown's veto. But as I argue at length in this paper, law enforcement agencies have reason to be concerned as well. In the absence of legislation that restricts the government's ability to use drones, the courts may attempt to step in and fill the void. There are undertones in recent Fourth Amendment cases that may call for restriction on government surveillance when permissive surveillance is conducted for such a long time that it becomes a Fourth Amendment search. Orin Kerr labels this view the "Mosaic Theory" of the Fourth Amendment.
In the absence of laws that regulate law enforcement drone use, courts may try to take up the task of restricting government drones by expanding Fourth Amendment doctrine. But the courts are ill-equipped for this task, since there is no clear legal basis for expanding Fourth Amendment protections and because courts do not have the technological know-how to determine just how far their restrictions on emerging drone technology may extend. Accordingly, law enforcement agencies should support legislative regulation on drones. Vetoes that leave the courts with the final word on drone technology create a risk of uncertain legal outcomes that may hinder law enforcement interests.
I have acknowledged that AB 1327 had shortcomings. But I think that Governor Brown's reason for vetoing the bill is dangerously broad. At some point, government technology should be regulated through legislation. The Fourth Amendment is becoming increasingly ill-suited to prevent emerging technology from violating privacy. To avoid strained, overly-broad, and potentially irreversible interpretations of the Fourth Amendment, states should enact legislation that increases privacy protection, while giving the government leeway to use new technology to enforce the law.