What police actually use it for
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Hot list match
A stolen vehicle passes a camera and an alert fires.
Legitimate
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Amber and Silver alerts
A missing child, or a missing adult with dementia, matched against a live list.
Legitimate
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Active lookout
A specific vehicle wanted in a specific crime, right now.
Legitimate
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Retroactive search
Everywhere a plate has been for the last thirty days. Every vehicle that passed an intersection between eleven and one.
A general warrant
The fourth is only possible if the movements of everyone were stored in advance, in case some of it mattered later. Collect on all, decide relevance afterward. That is the thing the Fourth Amendment was written against, and it is also the actual product being sold.
The mechanism
Match at the edge. Destroy on no match.
The camera holds the list on the device. A plate passes, it is compared locally, and if there is no match the read is destroyed where it was made. It is never transmitted, never stored, never becomes a record anywhere.
A city running a thousand cameras with eleven hits that day holds eleven records that day. Not four million.
Retroactive search does not need to be prohibited. There is nothing left to search.
The controls, and what each one forecloses
Hashed watch lists
The device holds one-way hashes, not readable plates. It can confirm a match. It cannot be read out as a list of who is being sought.
ForeclosesA seized, stolen, or subpoenaed device yielding a target list.
Signed device attestation
Each camera publishes a signed statement of its own configuration: which list it runs, which features are enabled, what it retains. A city can prove nationwide lookup is off instead of taking a vendor's word.
ForeclosesA vendor-side change silently re-enabling nationwide query, as happened in Ventura County, California, where the county reported a large volume of unauthorized accesses before the change was discovered.
Warrant-gated tracking with cryptographic expiry
Following a specific vehicle over time requires a warrant. The authorization carries a hard expiry the device itself enforces. A judge grants ten days and the device stops on the eleventh.
ForeclosesIndefinite tracking sustained by administrative renewal. The limit is not a policy anyone has to honor. The key stops working.
Court-held keys for any buffer
Where a jurisdiction insists on a short buffer for a scene canvass, it stays encrypted at the edge under a key held by the court, not by the agency and not by the vendor. Nobody browses it. A judge unlocks one place and one window.
ForeclosesRetroactive search becoming a routine desk tool rather than a judicial act.
Jurisdiction enforced by keys
A hit is encrypted to the key of the jurisdiction that issued the list entry. Sharing outside it is not a setting anyone can toggle.
ForeclosesLocal data reaching out-of-state agencies against state law because sharing was a checkbox, as alleged in California's action against the City of El Cajon.
Public audit by default
Every list addition, every hit, every warrant grant and expiry, published in aggregate as it happens. No request required.
ForeclosesPlates approved onto a watch list with no written policy governing who decides, or why, or for how long.
Our commitment
This is the system PACN builds, publishes as an open standard, and holds itself to first. Any vendor may implement it. Any city may require it. We would rather the standard win than the product.