A blow and go device is the common nickname for an ignition interlock device, or IID: a court-ordered breathalyzer wired into your car that keeps the engine from starting unless you blow a clean breath sample. The handheld unit is about the size of an older cellphone and sits in a cradle on your dashboard, connected by a coiled cord to a control box hidden underneath. Blow into the mouthpiece, register a blood alcohol concentration below the preset limit (usually 0.02 g/dL, essentially zero drinks), and the ignition unlocks. Courts in all 50 states can order one after a DUI, and 31 states plus Washington, D.C. require one for every first-time offender.1National Conference of State Legislatures. State Ignition Interlock Laws2Centers for Disease Control and Prevention. Increasing Alcohol Ignition Interlock Use
What the Device Looks Like in Your Car
The part you touch is the handheld unit. Picture an older flip phone or a compact TV remote. On top is a removable mouthpiece. On the face is a small LCD or LED screen that walks you through each step with prompts like “BLOW,” “PASS,” or “FAIL,” plus a button or two for navigating menus. A coiled cord, similar to an old telephone handset cord, runs from the bottom of the unit down to the control module. The cord is long enough to bring the mouthpiece to your face and short enough to tuck away when you’re not using it.
The control unit, sometimes called the ECU, is a small box wired into your vehicle’s ignition circuit, tucked beneath the dashboard where you won’t see it. A certified technician installs it by splicing into the wiring between your ignition switch and starter motor. When the ECU reads alcohol above the threshold, it blocks the signal to the starter and the engine won’t turn over. The control unit also stores a detailed log of every breath test, every violation, and any sign of tampering, all of which gets downloaded at your next service appointment.
Many states now require a small camera as part of the system. It mounts on the windshield or near the device and photographs the driver’s seat each time a breath sample is given, so the monitoring authority can confirm you were the one blowing.
How You Blow Into It
You don’t just exhale. Most devices require a specific breath pattern so that a balloon, an air compressor, or another person can’t fool the system. The most common pattern is a “blow-hum”: blow steadily into the mouthpiece for a couple of seconds, then transition into a humming sound, like saying “whooooo” like an owl, until you hear a click from the device. Some programs use a blow-only or hum-only pattern instead. Either way, the device needs a real, sustained breath delivered at a steady flow rate.3Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices
If a medical condition reduces your lung capacity, some states will approve a reduced breath volume requirement with physician documentation and court or licensing-authority approval.
Starting the Car
You’ll run through the same short sequence every time you drive. Turn the key or press the start button. The device powers on, beeps, and prompts you to blow. You give your breath sample. The whole thing takes about five to ten seconds. If your BAC reads below 0.02 g/dL, the screen shows a pass and the ignition unlocks.2Centers for Disease Control and Prevention. Increasing Alcohol Ignition Interlock Use
If the device reads alcohol above that threshold, you get a fail and the vehicle won’t start. You can wait a few minutes and try again, but a second failure triggers a longer lockout. States set their own escalation rules, with some running from a few minutes up to 30 minutes or more after repeated failures. After a certain number of consecutive fails, some states require you to bring the device in for servicing before you can try again.
Retests While You’re Driving
The device keeps monitoring after you’re on the road. At random intervals, it will beep and prompt you to blow again. These rolling retests are designed to catch someone who had a sober friend start the car or who started drinking after the initial test. You’ll have somewhere between 3 and 15 minutes to provide the sample, depending on your state.
You don’t need to pull over. The cradle sits within easy reach so you can blow while keeping your eyes on the road. If you fail a rolling retest or ignore the prompt, the device won’t shut off your engine, which would be a safety hazard. Instead, it logs the violation and triggers an alarm (typically the horn honking and lights flashing) until you turn off the ignition or provide a clean sample. That violation goes straight into the data log and gets reported at your next service visit.
What Can Trigger a False Fail
Mouthwash is the single most common culprit. Many popular brands contain between 14 and 27 percent alcohol, which is enough to register on the device even though you haven’t been drinking, and the alcohol can linger in your mouth for 15 minutes or more. The simplest fix is to switch to an alcohol-free brand. If you keep using regular mouthwash, rinse thoroughly with water and wait at least 15 minutes before blowing.
Other products that cause problems include certain breath sprays, some cough medicines, and fermented foods. The rule is simple: if it contains alcohol, keep it away from your mouth for at least 15 minutes before any test. If you get a fail you believe is false, rinse your mouth with water, wait for the lockout to clear, and try again. The device will log the first failure, but a clean retest helps show it wasn’t actual drinking when the data gets reviewed.
Service Appointments and Data Reporting
You have to bring the vehicle to an authorized service center on a regular schedule. The federal model specification requires the device to hold calibration for at least 37 days, and most states set service intervals somewhere between 30 and 90 days.3Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices Miss an appointment and the device can lock out your vehicle entirely.
At each visit, a technician recalibrates the breath sensor and downloads every record the control unit has stored: passed tests, failed tests, missed retests, and anything that looks like tampering. That data gets sent to whoever is monitoring your case, whether that’s the DMV, a probation officer, or the court. Repeated violations or signs of bypass attempts can lead to an extended IID requirement or a probation revocation hearing.
How Long You’ll Have It
Program length turns on the offense and the state. A first-time DUI offender might carry the device for as little as 90 days in one state or as long as three years in another. Repeat offenses push the requirement up, and in some states a third or fourth offense can mean three to five years with an interlock.1National Conference of State Legislatures. State Ignition Interlock Laws Violations during the program (failed tests, missed service appointments, tampering attempts) can extend the term beyond its original end date.
What It Costs
You pay for everything. Installation runs roughly $70 to $150, and the monthly lease and monitoring fee typically lands between $60 and $90. Over a six-month program, total costs commonly add up to somewhere in the $430 to $630 range once installation, calibration, monitoring, and any penalty fees are included. Some states offer financial hardship programs or reduced-fee arrangements for drivers who can’t afford the standard rates. Ask the court or your IID provider whether you qualify.
Tampering Consequences
Trying to disconnect, bypass, or trick the device is one of the worst decisions you can make. The control unit logs any power interruption, any attempt to disconnect wiring, and any breath pattern that looks like someone other than the driver is blowing, which is exactly why the camera exists. Tampering or circumvention is a criminal offense in most states, often charged as a misdemeanor carrying up to a year in jail. A tampering finding can also extend your IID requirement, re-suspend your license, or trigger a probation violation that puts you back in front of a judge for resentencing on the original DUI.
Having someone else blow for you counts as circumvention, and in states with camera-equipped devices the photos make that easy to prove. Even subtle attempts, like briefly disconnecting the battery, leave a clear footprint in the logs that technicians and monitoring authorities will see at the next service visit.