What an interlock device is and why it's installed
An interlock device is a breath-testing machine wired into your car's ignition. Before the engine starts, you blow into it. If the device detects alcohol above a set limit — usually 0.02% blood alcohol content — the car will not start. The device records every test you take, and those records go to the court or your state's Department of Motor Vehicles.
Interlock is ordered by a judge as a condition of a suspended license, usually after a DUI or DWI conviction. It is not a punishment on top of suspension — it is often the path back to driving during the suspension period. Some states require it; others make it optional. The judge decides whether you get one and for how long.
The device costs money to install, maintain, and remove. You pay these fees yourself. Installation typically runs $100 to $300, and monthly monitoring fees are usually $60 to $100. You also pay to have it removed when the court says you can.
Key Takeaways
- An interlock device lets you drive during a suspended license if a judge orders it as part of your sentence.
- You must pass a breath test before the engine starts each time, and the device records all tests for the court.
- You pay all costs — installation, monthly fees, and removal — out of your own pocket.
- Failing a test, tampering with the device, or missing a monitoring appointment can extend your suspension or result in new charges.
- The length of time you must use the device depends on your conviction and your state's law, not on how long your suspension lasts.
How the device works day to day
When you get in your car, you turn the key to the "on" position. The interlock device will prompt you to blow into the mouthpiece. You blow steadily for several seconds. The device measures your blood alcohol content and either allows the engine to start or locks it.
If you pass, the engine starts normally. If you fail, the ignition stays locked. Most devices give you a short window to try again — usually 5 to 10 minutes. After that, you have to wait longer before the next attempt. Repeated failures in a short time can trigger a "lockout" that requires you to visit a service center to reset the device.
While you are driving, the device may ask for a "rolling retest" — another breath sample while the car is moving. This prevents someone else from blowing into the device before you drive. If you do not provide a rolling retest when prompted, the device logs it as a violation, and the car may honk the horn or flash the lights to alert you.
Every test — passed or failed — is recorded with a timestamp. The service center downloads these records monthly and sends them to the court or DMV. Your driving record during the interlock period becomes part of your official file.
What happens if you fail a test or miss monitoring
A single failed breath test does not automatically end your driving privileges. However, multiple failures in a short time, or a pattern of failures, can trigger a violation report to the court. The court may then extend your interlock requirement, extend your suspension, or issue a new charge.
Missing a monthly monitoring appointment is treated more seriously. The service center will report you to the court as non-compliant. This can result in an extension of your interlock period, a new suspension, or even a warrant for your arrest, depending on your state and the terms of your sentence.
Tampering with, disabling, or attempting to bypass the device is a separate crime in most states. This includes asking someone else to blow into it for you, disconnecting wires, or using a device designed to fool the interlock. These actions can result in new criminal charges on top of your original conviction.
How long you must use the device
The length of your interlock requirement is set by the judge at sentencing and is based on your conviction, your blood alcohol content at the time of arrest, and whether you have prior DUI or DWI convictions. It is not automatically tied to the length of your license suspension.
In many states, a first offense requires 6 months of interlock use. A second offense within 10 years may require 1 to 2 years. A third or subsequent offense can require 2 to 3 years or longer. Some states have mandatory minimums; others give judges discretion.
You cannot remove the device early just because your suspension period ends. You must complete the full interlock term ordered by the court. Once you have met all the requirements — a clean monitoring record, all fees paid, and the full time served — you can petition the court or DMV to have the device removed.
The cost of interlock and who pays
You are responsible for all interlock costs. Installation fees range from $100 to $300 depending on your vehicle and the service provider. Monthly monitoring and calibration fees typically run $60 to $100 per month. Removal costs another $50 to $150.
If your interlock period is 12 months, you could spend $800 to $1,500 total. If it is 2 years, that number doubles. Some service providers offer payment plans, but you still pay the full amount. A few states have programs that reduce fees for low-income drivers, but these are rare and have strict income limits.
The service provider is chosen by your state's DMV or court system. You do not get to pick the company, but you can ask about payment options when you call to schedule installation.
Driving with an interlock device
Once the device is installed, you can drive normally — as long as you pass the breath test. You can drive to work, to the store, to medical appointments, anywhere. There are no restricted hours or zones. The only rule is that you cannot drive if you have consumed alcohol.
If you are taking medication that contains alcohol — such as some cough syrups or mouthwashes — tell the service center. They can note it in your file. A failed test caused by medication is less likely to be treated as a violation if it is documented in advance.
You must keep all monitoring appointments. Miss one, and the court will be notified. You must also keep the device in working order — if it malfunctions, contact the service center when ready to have it repaired or replaced. A broken device does not excuse you from the requirement; it just means you cannot drive until it is fixed.
After the interlock period ends
When you have completed your interlock term, you do not automatically get your full license back. The device removal is one step. Your license status depends on whether your suspension period has also ended.
If your suspension is still active when your interlock term ends, the device comes off but you still cannot drive. If your suspension has ended, the device comes off and you can drive normally again. Check with your state's DMV to confirm your current license status before you schedule removal.
After the interlock is removed, there is no ongoing monitoring. Your driving record is clean as far as the device is concerned. However, the DUI or DWI conviction itself remains on your record and can affect insurance rates, employment, and other areas of your life for years.
Frequently Asked Questions
Can I drive someone else's car without an interlock device?
No. Your license suspension applies to you, not to the car. You cannot legally drive any vehicle — yours or someone else's — during your suspension period, whether or not an interlock is installed. Driving without the device is driving with a suspended license, which is a separate crime.
What if I cannot afford the interlock fees?
Contact the service center and ask about payment plans. Some providers will let you pay monthly fees in installments. A few states have hardship programs that reduce fees for drivers below a certain income, but these are uncommon. Ask your court or DMV whether your state offers one. If you cannot pay, you cannot legally drive, and the interlock requirement remains in place.
Does using interlock help my case or reduce my sentence?
No. The interlock is part of your sentence, not something that reduces it. Complying with the interlock requirement — passing tests and attending monitoring appointments — is what the court expects. It does not shorten your suspension or remove your conviction. However, a clean interlock record can be helpful if you later petition the court to reduce other penalties or restore your license early.
What if I move to another state while on interlock?
You must continue to comply with the original court's order. Contact the service center and your original court to find out how to transfer monitoring to your new state. Some states have reciprocal agreements; others require you to travel back for monitoring appointments. Failing to maintain the device in your new state is non-compliance and can result in new charges.
Can I have the interlock removed early if I have a clean record?
Only the court that ordered it can remove it early. You can petition the court with evidence of a clean monitoring record, but the judge is not required to grant it. Most courts enforce the full term. Ask your attorney or the court clerk what the process is in your jurisdiction and whether early removal is possible.