What You'll Learn

• What the UEI COA2 measures and its detection range
• How to pair the COA2 with measureQuick via Bluetooth
• Where the CO reading appears in the measureQuick gas furnace workflow
• CO safety thresholds and what action to take at each level
• How measureQuick uses ambient CO in the venting/combustion pass/fail evaluation
• The difference between ambient CO monitoring and flue CO measurement
• Calibration requirements and battery management

What You'll Need

• Device: iPhone (iOS 15+), iPad, or Android phone/tablet (Android 10+) with measureQuick v3.5.18 or later
• Account: Active measureQuick account
• CO monitor: UEI COA2 Personal CO Meter
• Prerequisite knowledge: Bluetooth pairing fundamentals (see Bluetooth Pairing Basics)
• Time: 10 minutes to read; 2-3 minutes for initial pairing

What the COA2 Measures

The UEI COA2 is a personal ambient carbon monoxide monitor. It measures CO concentration in the surrounding air in parts per million (ppm). This is not a flue gas analyzer. It does not insert into a vent pipe. It clips to your belt or pocket and monitors the air where you are working.

The COA2 auto-zeros on power up, which means it calibrates its baseline reading when you first turn it on. Turn the unit on in clean air before entering a building.

Step-by-Step: Pairing the COA2

Step 1: Power On the COA2

Turn on the COA2 in clean outdoor air. The unit performs an auto-zero calibration during startup. The three-color LED indicator lights up and the Bluetooth radio activates automatically.

Clip the COA2 to your belt, shirt pocket, or tool bag where it will be exposed to the ambient air around you.

[Visual Reference] The UEI COA2 is a small, lightweight device (roughly the size of a pager) with a belt clip on the back. When powered on and reading safe CO levels, the LED indicator glows green. The unit has no screen; it communicates readings wirelessly to measureQuick. Clip it to your belt, shirt pocket, or tool bag where it stays exposed to the ambient air around you during the service call.

Step 2: Open the Toolbox in measureQuick

In the measureQuick app, navigate to the Tools screen. Tap Add or Scan to search for nearby Bluetooth devices. The COA2 should appear in the available devices list as "COA2" or "UEi COA2."

Tap it to pair. The connection establishes in a few seconds.

measureQuick Toolbox showing UEi COA2 in the available devices list

Step 3: Confirm the Connection

Once paired, the COA2 appears in your connected tools list. measureQuick begins receiving live ambient CO readings immediately. The CO monitor runs continuously in the background while you work, regardless of which screen you are viewing.

Connected tools list showing COA2 with live CO reading of 0 ppm

Where CO Readings Appear in measureQuick

The COA2 feeds ambient CO data into two places:

1. Background monitoring. Once paired, measureQuick monitors CO levels continuously. If CO rises above a threshold, the app triggers layered alerts: on-screen warnings, haptic vibration, audible alarms, and Apple Watch notifications (if connected). These alerts fire regardless of what you are doing in the app.

2. Gas furnace workflow, combustion analysis section. When running a gas furnace test, the ambient CO reading appears in the combustion analysis section. measureQuick uses this reading as part of the venting subsystem evaluation. The app compares return air CO to supply air CO to determine whether the furnace is contributing CO into the conditioned space.

Gas furnace workflow showing ambient CO reading in the combustion analysis section

CO Safety Thresholds

measureQuick uses threshold-based alerts aligned to ANSI/BPI-1200 standards. When CO levels rise, the app does not just alarm. It tells you what to do.

When a CO event occurs during an active project, measureQuick automatically snapshots the event data, including the reading, threshold level, and timestamp, and uploads it to measureQuick Cloud. This creates a safety record without the technician needing to stop and document anything manually.

Ambient CO vs. Flue CO

These are two different measurements taken with two different instruments.

Ambient CO (COA2): Measures carbon monoxide in the room air where the technician is standing. This is a safety measurement. It tells you whether CO is present in the occupied space.

Flue CO (combustion analyzer): Measures carbon monoxide inside the vent pipe, in the exhaust stream leaving the appliance. This is a diagnostic measurement. It tells you how completely the appliance is burning fuel. Flue CO readings of 25 ppm or less (air-free) are considered normal. Readings above 100 ppm air-free indicate a problem with the appliance.

A combustion analyzer (such as a Sauermann Si-CA series) inserts a probe into the flue and measures CO, CO2, O2, stack temperature, and draft. The COA2 clips to your belt and monitors the air around you. They serve different purposes and both are part of a thorough gas furnace evaluation.

measureQuick evaluates both measurements when available. The ambient CO reading from the COA2 contributes to the venting subsystem pass/fail (pf_venting) by confirming whether combustion byproducts are escaping into the living space. The flue CO reading from a combustion analyzer evaluates the appliance's combustion quality.

Calibration and Maintenance

Auto-zero: The COA2 auto-zeros every time it powers on. Always turn it on in clean outdoor air before entering a building. If you power it on in a space that already has elevated CO, the baseline will be wrong and the readings will be inaccurate.

Annual calibration: UEI recommends professional calibration once per year. This involves exposing the sensor to a known concentration of CO gas and verifying the reading. Contact UEI or an authorized service center for calibration.

Sensor self-test: The COA2 includes an integrated CO sensor self-test function. Run it periodically to confirm the sensor is responding correctly.

Battery life: The COA2 runs on 3x AAA batteries. Carry spares. The unit has an auto power-off feature that can be disabled if you want it to run continuously during a long job.

Storage: Store the COA2 in a clean, dry environment. Do not leave it sealed in a toolbox with solvents, adhesives, or other chemicals that could degrade the sensor.

Video Walkthrough

• YouTube: - Jim Bergmann demonstrates a live CO alarm event, walks through the alert system, threshold-based action guidance, and cloud logging

• YouTube: - Jim Bergmann and Louise Kellar (UEI National Training Manager) cover the COA2, SPMKIT, and DPM integrations

Tips & Common Issues

COA2 reads 0 ppm but I know there is CO present

Confirm the unit auto-zeroed in clean air. If you powered it on indoors where CO was already present, the baseline is skewed. Power the unit off, take it outside, and power it back on in fresh air. Wait for the startup sequence to complete before re-entering the building.

Alerts are not appearing in measureQuick

Verify the COA2 is connected in the Toolbox (green status indicator). Check that notifications are enabled for measureQuick in your phone's settings. On iOS, confirm that measureQuick has permission for notifications, sounds, and haptic alerts. If using an Apple Watch, verify the measureQuick watch app is installed.

Should I use the COA2 instead of a combustion analyzer?

No. The COA2 measures ambient CO in the room. A combustion analyzer measures flue gas composition inside the vent pipe. You need both for a complete gas furnace evaluation. The COA2 monitors your safety while working. The combustion analyzer diagnoses the appliance.

The COA2 alarm went off at a low reading

The built-in audible alarm on the COA2 hardware activates at 35 ppm. measureQuick's software alerts begin at 9 ppm (elevated). The app-based alerts are more granular than the hardware alarm because they include threshold-specific action instructions. Rely on the measureQuick alerts for context-aware guidance.

Related Articles

Prerequisites (complete these first):

• Bluetooth Pairing Basics

Follow-up articles (next steps after this one):

• Sensorcon CO Meter - Alternative ambient CO monitor
• Combustion Analysis Fundamentals - Full combustion testing with a flue gas analyzer
• Bluetooth Troubleshooting

Related in the same domain:

• Smart Tool Overview
• Tool Selection Guide

Related in other domains:

• Combustion Probe Placement
• Gas Furnace Workflow

Need Help?

If you get stuck or this article does not answer your question:

• Check the Related Articles section above
• Contact measureQuick support: support@measurequick.com
• Schedule a training session with our support team