Texas Ignition Interlock Device Requirements

An ignition interlock device is a breathalyzer wired into your vehicle's ignition system. You blow into it before the engine will start, and it requires periodic retests while you're driving. In Texas, an IID requirement is tied to specific DWI conviction circumstances, and the rules around how it interacts with your license, your ODL, and your employer's vehicles are more nuanced than most people realize.

When Texas Requires an IID

An ignition interlock device is mandatory for:

• First-offense DWI with a BAC of 0.15% or higher. The elevated BAC alone triggers the IID requirement, even without aggravating factors.
• Any second or subsequent DWI conviction. Prior offenses don't have to be recent — a DWI from 15 years ago still counts as a prior for interlock purposes.
• Any DWI involving a motor vehicle crash. If the DWI arrest resulted from or included a collision, the court must order an IID regardless of BAC level.
• Any DWI with a child passenger. DWI with a child passenger (under 15) is charged as a state jail felony and carries a mandatory IID requirement.

Courts can also order an IID at their discretion for first-offense DWI convictions with a BAC below 0.15%, particularly as a condition of bond or probation. The mandatory categories above are the cases where the judge has no choice.

The Restricted Interlock License

Under Transportation Code § 521.2465, when a court orders an IID restriction, DPS cancels your regular license 30 days after receiving the court order — unless you apply for a restricted interlock license within that window.

The restricted interlock license replaces your standard license and displays a specific restriction code indicating the IID requirement. To apply, mail the application and proof of IID installation to DPS. The physical card arrives by mail after DPS processes the request, which takes approximately 21 business days.

While the restricted interlock license is active, you can only legally drive vehicles equipped with a functioning IID. The device must be calibrated and maintained by a certified provider at regular intervals (typically every 30 to 60 days).

The Employer Vehicle Exception

Here's the part that matters most for people who drive company vehicles: Texas allows a "P39 employer restriction" for drivers with an IID requirement who need to operate an employer-owned vehicle for work. This exception lets you drive your employer's non-interlock vehicle during working hours, provided:

• Your employer is aware of your interlock restriction
• You carry an official letter on company letterhead confirming the employer's awareness
• The vehicle is owned or leased by the employer (not your personal vehicle)
• You are operating it during the course of employment

This exception exists because requiring an employer to install an IID on a fleet vehicle — a truck, delivery van, or service vehicle used by multiple employees — would effectively prevent the restricted driver from working.

The employer exception is not available to CDL holders. If you hold a commercial license and have an IID restriction, you cannot operate any commercial motor vehicle under the ODL or the interlock license.

ODL Interaction: No Geographic or Time Restrictions

One important benefit of the IID: if your Occupational Driver's License has an interlock restriction, the court is prohibited from imposing geographic or hourly driving restrictions. Under Transportation Code § 521.248(d), a driver with an IID-restricted ODL can drive at any time of day and to any location for any qualifying essential purpose.

This is a significant practical advantage over a standard ODL, which limits driving to a maximum of 4 hours per 24-hour period (or 12 hours if the court grants an extended schedule) and can restrict travel to specific counties.

Costs to Expect

IID installation runs $70 to $150 depending on the provider and vehicle. Monthly monitoring and calibration fees add $60 to $90. Over a one-year IID period, total costs typically fall between $800 and $1,200.

Some providers offer income-based assistance programs. If the court finds you indigent, they can order fee reductions or refer you to a provider with a sliding-scale payment option.

The Texas Driver's License Reinstatement Guide covers the full DWI reinstatement pathway including IID requirements, the restricted license application process, and how the employer exception interacts with your specific suspension type.

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