An ignition interlock device (IID) is a breath tester wired into your vehicle's ignition: blow a clean sample, and the car starts; blow alcohol, and it doesn't — and the attempt is logged. For many Texas DWI defendants, interlock is the single most intrusive daily consequence of the case.
When interlock is required
Interlock is mandatory for second and subsequent DWI convictions, and commonly ordered when the BAC was 0.15 or higher, as a condition of bond (especially in Dallas County high-BAC and repeat cases), and as a condition of an occupational license. Whether it's imposed — and for how long — is one of the negotiable points in a DWI case, which makes it a real defense issue, not just an administrative one.
Day-to-day reality and cost
Budget roughly $70–$100 per month for leasing and monitoring, plus $100–$150 for installation — over a year, interlock commonly runs $1,000 or more. The device requires rolling retests while driving, monthly calibration visits, and careful habits: mouthwash, some medications, and even certain foods can register alcohol. Test failures and missed retests are recorded and reported.
What counts as a violation
Failed startup tests, failed or skipped rolling retests, tampering, and missed service appointments all generate reports to the court or your supervision officer. Violations become leverage for prosecutors and can extend the requirement — or, on bond, send you back to jail. Having someone else blow into the device is a separate criminal offense for both of you.
Getting it removed
Interlock removal is not automatic at the end of the required period. A judge must sign a removal order — your attorney files the motion, and the court may review your device data for violations before signing. Only after the order should the vendor uninstall the unit, and keep the paperwork: DPS records can lag behind the court file.
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