How we check the numbers

State rules

For each state we read the statute and the page of the agency that runs the interlock program. Every fact on a state guide carries the sentence it came from and a link to the page; press the small "source" button next to any fact to see it. Each guide shows the date we last checked it. Where we couldn't confirm something from an official source we leave it out, which is why some states have a shorter "basics" page while we finish them.

The national map and the state table use the IIHS review of interlock laws. IIHS counts a state when an interlock is required to drive during a post-conviction suspension, or to get the license back. Courts can order one in other ways too, so we say so wherever the map appears.

Approved companies

Approvals come from each state's own list of approved devices or providers, and company marketing doesn't count. We've read 44 of those lists so far. When a company has changed its name (Dräger's US interlock business now operates as RoadGuard), we count both names as one company.

Prices and fees

Advertised prices are what a company showed for a given state on the date we list. Most companies don't publish their full fee list, so we also use the fee schedules they file with New York State, which cover items like lockout resets, missed appointments, removal and lost equipment. Those amounts apply in New York and carry the filing date, so you can tell an old schedule from a current one.

Device details

Device features come from company manuals, spec sheets, FAQ pages and state certification documents, each linked from the company page. The handset drawings are our own illustrations based on the companies' product photos; we use real photos only where they're openly licensed.

Writing

We use AI tools to draft plain-English summaries from the verified facts. A script then checks that every number in the text appears in the cited source, and anything that fails gets fixed before it's published.

Corrections

If you find a mistake, send it to us with a link to the source and we'll fix it and update the date.