how does a breathalyzer in a car work

[EleanorRose]

A car breathalyzer, formally known as an ignition interlock device (IID), works by preventing a vehicle from starting if it detects a blood alcohol concentration (BAC) above a pre-set limit, typically 0.02%. It's a complex system that combines breath analysis technology with your car's ignition system.

Here's the step-by-step process:

1. The Test: Before you can start the car, you must blow into the handheld unit. The device uses a fuel cell sensor to analyze your breath sample. This sensor is specifically designed to react with ethanol molecules, creating a small electrical current. The strength of this current is directly proportional to the amount of alcohol in your breath.
2. The Analysis: The device's internal computer calculates your estimated BAC based on the sensor's reading.
3. The Decision: If your BAC is below the limit, it sends a signal to the vehicle's ignition system, allowing you to start the engine. If it's above the limit, the ignition remains locked.

The system also includes rolling retests to prevent a sober person from starting the car for an intoxicated driver. While driving, you'll be prompted to provide another breath sample at random intervals. Failure to take or pass this test triggers a series of warnings (like flashing lights and honking horns) meant to encourage you to pull over safely; it does not turn off the car, as that would be a safety hazard.

Feature	How It Works	Purpose
Initial Test	Blow into the handset before starting the engine.	Prevents the car from starting if alcohol is detected.
Fuel Cell Sensor	Electrochemically oxidizes alcohol, creating a measurable current.	Provides accurate and specific BAC readings.
Rolling Retest	A prompt to give another sample while driving, usually within 5-20 minutes.	Ensures the driver remains sober throughout the trip.
Violation Logging	Records all test results, passes, fails, and attempts to bypass.	Provides data for legal authorities or monitoring agencies.
Calibration Requirement	Requires professional service every 30-120 days.	Ensures the device maintains accuracy over time.

These devices are typically court-ordered for individuals convicted of driving under the influence (DUI). The goal is to allow individuals to continue driving for work and essential tasks while ensuring public safety.

[KalebLee]

I had one in my car for six months after my DUI. You blow into it like a straw, and it’s got a little fan that whirs. It’s not just a one-time thing at startup, either. It’ll beep at you while you’re driving to give another sample. It’s a constant reminder. The worst part is the calibration appointments you can’t miss. It’s a hassle, but it definitely keeps you in check. You just don’t risk it.

[StEmilia]

From a technical standpoint, it's a simple closed-loop system. The breath sample is the input. A specialized sensor, often a fuel cell, acts as the processor to measure alcohol content. The output is a signal to the car's ECU. If the analyzed data is within the allowed parameters, the ECU enables the starter circuit. If not, it remains open. The system's sophistication lies in its anti-circumvention features and tamper-proof data logging, not just the basic breath test.