What Is An Ignition Interlock Device?


Tennessee law requires the use of an Ignition Interlock Device (“IID”) for most motorists upon conviction of Driving Under the Influence (“DUI”).  The requirement of an IID generates many questions for TN motorists.  Primary among the questions is: What is an Ignition Interlock Device?

Tennessee Department of Safety and Homeland Security High Patrol Division Rule 1340-03-06-.02 defines an Ignition Interlock Device as “a device that is designed to allow a driver to start a vehicle if the driver’s [Breath Alcohol Concentration (“BrAC”)] is below the set point and to prevent the driver from starting the vehicle if the driver’s BrAC is at or above the set point.”  

An IID is essentially a breath alcohol test device that requires a driver to register a breath test sample not only prior to starting the vehicle, but also periodically while operating the vehicle, to verify that the driver’s breath alcohol concentration remains below a preset level.  Tennessee law requires Ignition Interlock Devices be calibrated to a setting of .02%.  Accordingly, should the driver register at or above .02%, the IID will prevent the vehicle from being started. 

In the coming weeks, this blog will address additional questions surrounding the Tennessee IID requirements, including, but not limited to: When is an IID required? Is an IID mandated even when a DUI conviction does not involve alcohol? What procedures must be met to have an IID removed from a motorists’ vehicle? What are the consequences an Ignition Interlock Device violation?

In the meantime, should you have any questions relating to a Tennessee DUI arrest, the lawyers at Oberman & Rice are available to speak with you at (865) 249-7200.

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