New Hampshire Ignition Interlock — Requirements & Costs

An ignition interlock device (IID) is a breathalyzer wired into your vehicle's ignition system. It prevents the engine from starting if it detects alcohol on your breath above a preset threshold §265-A:36; §265-A:18. In New Hampshire, IID requirements are a central part of DWI consequences.

not mandatory for a simple first offense — the court may, in its discretion, require an interlock during the period of sentence reduction (RSA 265-A:18, I(a)(6)(A)).

aggravated or subsequent DWI: not less than 12 months nor more than 2 years after the period of revocation or suspension; under 21: until age 21 or at least 12 months, whichever is longer. Where an interlock is required, a certificate proving installation is a condition precedent to reinstatement..

Common violations that can extend the IID period or trigger additional consequences:

• Failed startup tests (BAC above threshold)
• Failed rolling retests
• Missed calibration appointments
• Tampering with or attempting to circumvent the device
• Operating a vehicle without an IID when one is required

IID costs are borne by the offender and include:

• Installation fee
• Monthly monitoring/rental fee
• Removal fee
• Calibration fees (may be included in monthly rental or charged separately)

While the IID is a restriction, it is also the mechanism that allows many offenders to resume driving sooner than they would under a full suspension. In New Hampshire, restricted driving privileges during the suspension period are limited. Complying fully with IID requirements — no violations, on-time calibration — is the fastest path to full reinstatement.