Until Flock, the vast majority of those cameras were privately owned and not integrated into any larger network. If the police wanted camera data, they had to ask businesses or homeowners, and there was no regulation of data retention, so if they wiped their recordings after 48 hours, there was nothing the police could do about it.

It's the aggregators of that data that are the real risk, not doorbell cams or shopkeepers trying to limit shoplifting or vandalism.