Usually yes. Most consumer CO2 monitors use NDIR sensors that drift slightly over months of use, so they rely on periodic recalibration to stay accurate. Many do this automatically, assuming the lowest reading they see over a week reflects fresh outdoor air; you can also trigger a manual calibration outdoors.
What is ABC calibration for a CO2 monitor?
ABC stands for Automatic Baseline Calibration. The monitor assumes that at some point each week a room ventilates down to roughly fresh-air carbon dioxide levels, and quietly resets its baseline to that lowest recorded value, correcting slow sensor drift on its own.
ABC keeps readings honest without any effort from you, which suits living spaces that get aired out regularly. Its assumption is simple but usually safe: no occupied room stays sealed and stuffy every hour of every day.
Most consumer monitors run this correction on a rolling seven- to fourteen-day window, so a couple of well-ventilated days within that stretch is usually enough for the baseline to stay accurate.
NDIR sensor and ppm accuracy
Most reliable CO2 monitors, including models from Aranet and Temtop, use an NDIR sensor, which reads gas concentration in ppm by measuring how much infrared light carbon dioxide absorbs. NDIR accuracy is generally strong, but it still drifts slowly and needs the periodic correction ABC or manual calibration provides. Cheaper sensors using other technologies are typically less stable over time than NDIR, which is why most trustworthy monitors settle on it.
When does automatic calibration go wrong — classroom and office spaces?
In rooms that never fully ventilate — a bedroom occupied every night, a busy classroom, or a windowless office — the weekly low never reaches true fresh air. ABC then anchors its baseline too high, making real CO2 look lower than it actually is.
For those spaces, disabling ABC and calibrating manually gives a truer read. Continuous occupancy is exactly where an accurate CO2 number matters most, since a falsely low baseline undermines the whole point of monitoring a busy room.
A grow tent or a small windowless office are two of the clearest real-world cases where ABC quietly drifts upward for weeks without anyone noticing, until a manual check outdoors reveals the gap.
Ventilation, carbon dioxide, and indoor air quality
Carbon dioxide is one of the simplest proxies for ventilation and general indoor air quality, since it climbs predictably as people breathe in a closed space and drops once fresh air replaces it. A classroom or office that stays a poorly calibrated monitor's blind spot loses that early warning entirely, since a reading that looks fine actually hides steadily worsening ventilation.
How do you calibrate one manually?
Take the monitor outdoors, away from your own breath and any exhaust, and let it sit in open air for several minutes. Then run its calibration routine, which tells the sensor to treat the current reading as the fresh-air baseline near 400 to 420 ppm.
Doing this every few months, or after moving the device, keeps readings trustworthy. It is a two-minute task that resets the reference point the whole measurement depends on. INKBIRD and Vitalight both document this manual process in their monitor manuals for exactly this reason. Note the date when you calibrate so you can track whether the interval you are using actually keeps drift in check over a full year.
Real-time data logging and alerts
A monitor's real-time display is only half the value; data logging that stores hours or days of history lets you see when levels actually spike, such as during a packed meeting or a closed-door class period. Alerts that push a notification past a set point catch problems even when nobody is watching the screen. Reviewing a week of logged data after installing a monitor in a new room is a fast way to learn its normal pattern before trusting any single reading.
Does temperature, humidity, or an alarm threshold affect readings?
Temperature and humidity do not directly change a properly functioning NDIR sensor's CO2 reading, but many monitors log them alongside carbon dioxide anyway, since all three shape how stuffy or comfortable a room feels together.
Setting an alarm threshold — commonly around 1,000 to 1,500 ppm — turns passive monitoring into an active nudge to open a window or door, which is the whole practical point of owning one of these sensors in a classroom, office, or bedroom.
A well-calibrated monitor with a sensible threshold turns an invisible problem into a simple, visible signal, which is ultimately more useful day to day than chasing lab-grade precision on the raw ppm number.