How a Vehicle Alcohol Interlock Works

The Start Sequence and What Happens After the Driver Blows

The driver approaches the vehicle, picks up the handset, and blows into it. The system checks the handset's readiness. If the unit is within its 12 month calibration interval and the temperature is within -20 to 65 C, the handset signals that it is ready to test. The driver blows into the handset. The fuel cell sensor measures ethanol concentration in the breath sample. The result is displayed on the handset screen. If the reading is below the alarm threshold, the vehicle starts. If it is above, the system locks the start circuit and displays an alarm.

Read the Alcohol Interlock ALC-303 specification →

Readiness Time in Cold Weather and What It Means for Operations

At -40 C, the handset takes up to 180 seconds to become ready. At -20 C, it takes 120 seconds. At 25 C, it takes approximately 1 second. This delay is due to sensor warm-up and internal system checks. In cold climates, the system must be powered on at least 15 minutes before use to ensure readiness. The control box remains powered during the vehicle's idle state. If the vehicle is turned off, the system must re-warm before the next test.

Read the Alcohol Interlock ALC-308 specification →

Retest During a Journey and How the System Enforces Compliance

If the vehicle is running and the system detects a new breath sample above the threshold, it triggers a retest. The driver is prompted to blow again. If the second test is above the threshold, the system logs the event and may disable the vehicle after a set number of failures. The system does not allow the vehicle to restart until the next scheduled test or until the unit is reset by a service technician. Retests are logged and stored in the control box memory.

Read the Alcohol Interlock ALC-303 specification →

What the Log Contains and Who Reads It

The control box stores a log of every test, including the timestamp, result, temperature, alarm status, and whether the vehicle started. It also records retests, failed attempts, and system resets. The log is accessible via RS-485 or RS232 to external systems such as fleet management software. The data is used by safety officers, fleet managers, and compliance auditors to verify that the system is functioning and that drivers are complying with the policy.

Read the Alcohol Interlock ALC-308 specification →

Fitting and Commissioning on 9V and 36V Vehicles

The control box connects to the vehicle's start circuit using a relay. For 9V systems, the control box uses a 9V DC power supply. For 36V systems, it uses a 36V DC supply. The wiring must be isolated from the ignition circuit. The handset is mounted near the driver’s seat. The UART link between handset and control box is shielded. Commissioning requires verifying the power supply, signal integrity, and correct relay operation. The system must be tested after installation to confirm the start circuit is properly blocked.

Read the Alcohol Interlock ALC-303 specification →