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What is an ignition interlock device?

An ignition interlock device (IID) is a breath-alcohol tester wired into a car's ignition. The car won't start until you blow a sample under the limit your state sets, and the device asks for more samples while you drive. Courts and state licensing agencies order them after DUI offenses, and you lease one from a state-approved company for the length of the order.

Updated Oct 23, 2026How we check

What the device looks like

Dräger Interlock 7000 handset and control unit
Handset and control unit. You blow into the handset; the control unit is wired to the starter under the dash. Dräger Interlock 7000 · Ninapayan, CC BY-SA 4.0
Guardian AMS2000 handset showing PASS
The handset. It shows pass or fail and prompts for retests. Guardian AMS2000 · Rsheram, CC BY-SA 3.0
Dräger interlock camera
The camera. Some states and configurations add one that photographs whoever gives the sample. Dräger camera · Ninapayan, CC BY-SA 4.0

How does an ignition interlock work?

  1. 1Blow before you startThe handset asks for a breath sample. If the alcohol reading is under the limit your state sets, the car starts.
  2. 2Retest while drivingA few minutes into the drive, and at random after that, the handset asks for another sample. You get a few minutes to give it, so you can pull over.
  3. 3Every test is loggedThe control unit under the dash records each sample, any fail and any missed retest, and many devices add a photo.
  4. 4Service visitsAt each calibration visit the service center checks the device and downloads the log for your court or state agency.
  5. 5RemovalWhen your order ends and your state signs off, the device comes out at a service center.

The limit is low. In Minnesota, for example, the device won't let the car start at a breath alcohol reading of 0.02 or higher.1 Your state guide lists your state's limit where the statute gives it.

How you blow and how long you get for a retest

The breath pattern and the retest window differ by company and state.

CompanyHow you blow
Smart Start
Blow and hum for 3 to 4 seconds. Some states use blow-inhale-blow, and the pattern depends on your state.2
Intoxalock
Blow, inhale, then blow again into the mouthpiece. No humming is mentioned.3
LifeSafer
Take a deep inhale, then blow and hum a consistent tone. The hum is saying "DO".4
Alcohol Detection Systems
The Determinator 2 asks for a blow / suck / blow sample.5
RoadGuard
RoadGuard says it is a simple blow-and-suck device.6
Low Cost Interlock
The LCI Co-Pilot uses a blow/hum or straight hum pattern, depending on your state.7
ALCOLOCK
On the ALCOLOCK GR (wireless), you blow while humming. The handset makes a tone to tell you the sample is proper.8
CompanyRolling retest window
Smart Start
5 minutes to respond once prompted, per a 2017 Kansas manual. Smart Start's current rules may differ.9
Intoxalock
6 minutes, according to the Intoxalock FAQ. Your state sets the actual rule.10
LifeSafer
3 to 10 minutes, depending on your jurisdiction.11
Alcohol Detection Systems
The time you get to give a rolling retest sample is typically 3 minutes.12
RoadGuard
RoadGuard says you will have "several minutes" to give the test. It gives no figure.13
Low Cost Interlock
The LCI-777 asks for a sample 5-7 minutes into a rolling retest. The device FAQ gives a minimum of 5.14

Ignition interlock installation

Installation happens at a service center certified by your state, usually run by or for the interlock company. Intoxalock says an install typically takes one to four hours.15 Bring your court order or DMV paperwork. After the install, most of the states we've checked issue a license with an interlock restriction, which is the license you drive on until the order ends; your state guide names it.

Who has to get one?

It depends on the state. Per the IIHS review (October 2026), 30 states and DC require an interlock after a first DUI conviction, 6 more require one for a first offense only at a high BAC, 7 require one only for repeat convictions, and 7 have neither requirement by the IIHS definition.16 Courts can also order one as a condition of bond or probation. Interlock laws by state

How much does an ignition interlock cost?

On the fee schedules companies file or publish, a 12-month order with lease, install and removal starts at about $1,205, before calibration visits and any lockout or missed-appointment fees. See ignition interlock cost for the full fee comparison and the cheapest interlock companies.

Which companies install them?

Each state approves its own list of companies, and you have to use one on it. The best ignition interlock companies ranks the eight most widely approved; every company also has its own profile.

Living with an interlock

More guides

Sources

  1. 0.02 or higherrevisor.mn.gov/statutes/cite/171.306
  2. Blow into the device for three or four seconds while humming at the same timesmartstartinc.com/ignition-interlock-devices
  3. blow, inhale, and blow again into the device’s mouthpieceintoxalock.com/ignition-interlock-devices/faq
  4. deep inhale, blow and hum a consistent tonelifesafer.com/devices
  5. providing a Blow/Suck/Blow samplenmtsc.unm.edu/wp-content/uploads/ADS-User-Manual-Determinator-2.pdf
  6. we have a simple blow and suck deviceroadguardinterlock.com
  7. Blow/Hum Techniquelowcostinterlock.com/wp-content/uploads/2025/05/LCI-Co-Pilot-User-Instructions.pdf
  8. then hum. The handset makes a tone to indicate propernmtsc.unm.edu/wp-content/uploads/GR-wireless-IRM-ENG-60-000139-E-Instruction.pdf
  9. Once prompted for a retest, you have 5 minutes toksrevenue.gov/doviidmanuals/SmartStart.pdf
  10. you’ll have a 6-minute window to provide a breath sampleintoxalock.com/ignition-interlock-devices/faq
  11. typically between 3 and 10 minutes, depending on your jurisdictionlifesafer.com/wp-content/uploads/2019/08/l250-clienthandbook.pdf
  12. The typical time allowed isnmtsc.unm.edu/wp-content/uploads/ADS-User-Manual-Determinator-2.pdf
  13. You will have several minutes to give the testroadguardinterlock.com/wp-content/uploads/2019/04/interlock-7000-if-en-user-manual_1.51.pdf
  14. 5 to 7 minutes to submit a breath samplelowcostinterlock.com/wp-content/uploads/2021/12/2016-11-09-LCI-777-User-Manual.pdf
  15. typically takes about one to four hoursintoxalock.com/ignition-interlock-devices/faq
  16. iihs.org/research-areas/alcohol-and-drugs/alcohol-interlock-laws-by-state