What Is an Ignition Interlock Device and When Is It Required?

Posted: June 02, 2026

An ignition interlock device (IID) is a breathalyzer installed in your vehicle that prevents the engine from starting if it detects alcohol on your breath. Tennessee law requires or allows the installation of these devices in connection with a DUI conviction, and the financial and personal burden of maintaining one can affect your daily life for months or even years.

How Does Tennessee’s IID Program Work?

Once the court orders installation, you must have the device placed in every vehicle you own or regularly operate at your own expense. The program involves ongoing obligations that continue throughout the entire monitoring period:

Monthly calibration and data download appointments at an approved service center
Random rolling retests while the vehicle is in operation
Payment of installation fees
Monthly monitoring fees
Immediate reporting of any failed tests or device malfunctions
Maintaining a violation-free record throughout the required term

Mandatory Ignition Interlock Device (IID) Installation

Under Tennessee Code Annotated § 55-10-417, IID installation is mandated for certain DUI offenses. The court has no discretion to waive the requirement. Situations that trigger automatic installation:

First-offense DUI with a blood alcohol concentration (BAC) of .15% or higher
All second DUI convictions
All third and subsequent DUI convictions
Any DUI involving a minor passenger under 18 years old
Vehicular assault convictions involving alcohol impairment

Court-Ordered (Discretionary) IID

Even when Tennessee law does not require an ignition interlock device (IID) installation, judges may still order one as a condition of sentencing. Courts often use this discretion in cases involving factors that indicate an increased risk of future DUI violations:

First-offense DUI with a BAC below .15%
Cases involving erratic or dangerous driving behavior
Defendants with a history of alcohol-related incidents
Situations where the judge believes monitoring will reduce the likelihood of reoffending
As a condition for granting a restricted driver’s license during the revocation period

IID as a Condition of Probation

Judges in Davidson County and throughout Middle Tennessee regularly impose IID installation as a probation condition, even when the statute does not specifically require it. Violating that condition can trigger a probation revocation hearing and potentially result in jail time for the underlying DUI sentence.

Penalties for Violating IID Requirements

Tampering with, circumventing, or failing to maintain your ignition interlock device carries its own set of penalties separate from the original DUI sentence. Tennessee treats IID violations seriously, and consequences can compound quickly:

Extension of the IID monitoring period
Additional fines imposed by the court
Revocation of your restricted driving privileges
Probation violation proceedings that may lead to incarceration
A new misdemeanor charge for tampering with or circumventing the device
Permanent notation on your driving record

The Final 120 Days: What You Must Do to Remove Your Ignition Interlock

Tennessee requires 120 consecutive days with no violations recorded on the device before removal. That means zero failed breath samples, no missed calibration appointments, and no evidence of tampering. A single violation during that window resets the 120-day clock entirely.

Our attorneys at Andrew C. Beasley, PLLC, help clients manage the IID process from installation through removal, address violations that arise, file motions to modify interlock conditions when appropriate, and work to prevent unnecessary extensions of the monitoring period. Call us at 615-846-9889 or reach out online to schedule your free consultation with our Nashville DUI lawyers today.