Is Temtop S1+ Accurate? How to Understand PM2.5 Monitor Readings Malaysia

Is the Temtop S1+ accurate, and why can its PM2.5 reading be different from another air-quality monitor or air purifier?

This is one of the most important questions to understand before using any consumer PM2.5 monitor.

The short answer is:

Two PM2.5 devices do not have to display exactly the same number every second for both readings to be useful.

Differences can occur because of:

Sensor technology

Measurement location

Airflow

Sampling conditions

Response characteristics

Internal processing

and

the fact that indoor PM2.5 itself is constantly changing.

The Temtop S1+ uses a laser-based particulate sensing system and provides PM2.5 readings across a specified range of:

0–999 μg/m³

with:

0.1 μg/m³ resolution.

For household use, the most useful approach is not to obsess over whether two devices differ by a small amount at one instant.

Instead, ask:

Does the monitor consistently show meaningful changes in the environment?

Accuracy and Resolution Are Not the Same Thing

Before discussing PM2.5 monitors, it is important to understand this distinction.

Resolution

Resolution describes the smallest displayed measurement increment.

For the S1+, PM2.5 resolution is specified as:

0.1 μg/m³.

But this does not mean:

the instrument has ±0.1 μg/m³ accuracy.

Those are different specifications.

Resolution ≠ Accuracy.

This is a common misunderstanding when comparing measuring instruments.

Why We Don't Claim an Unsupported PM2.5 Accuracy Number

When evaluating an instrument, specifications should come from reliable manufacturer information.

If a PM2.5 accuracy specification is not clearly established in the available product documentation, it should not be invented from the display resolution or assumed from another model.

Therefore, for the S1+:

Do not convert its 0.1 μg/m³ resolution into an accuracy claim.

Instead, understand the product according to its intended application:

practical consumer indoor PM2.5 monitoring and trend observation.

What Does a Laser PM2.5 Sensor Do?

A laser-based particulate sensor detects airborne particles passing through its sensing system and estimates particulate concentration.

This makes it possible to monitor changing indoor particulate conditions.

For example:

Cooking starts

↓

Particles increase

↓

PM2.5 reading rises

or:

Air purifier starts

↓

Particles are filtered

↓

PM2.5 reading falls

This ability to observe environmental change is one of the biggest practical benefits of a household PM2.5 monitor.

Why Two PM2.5 Monitors May Show Different Numbers

Suppose you put:

Temtop S1+

and

another PM2.5 monitor

in the same bedroom.

One shows:

12 μg/m³

while another shows:

15 μg/m³.

Does that automatically mean one is defective?

No.

There are several possible reasons.

Reason 1: The Sensors Are Not in Exactly the Same Position

Even if two monitors are placed on the same table, their sensing openings may be several centimetres apart.

Indoor air contains moving particles.

The air around each inlet is not necessarily identical at every instant.

This becomes even more noticeable if the devices are near:

Air-conditioning airflow

A fan

A purifier

A window

a doorway.

Reason 2: Indoor Air Is Not Perfectly Mixed

A bedroom is not a laboratory chamber with perfectly uniform particle concentration.

One side of the room may be closer to:

a window

while another is closer to:

an air purifier.

The doorway may introduce air from the living room.

The air conditioner may create circulation patterns.

Therefore:

Different location = potentially different PM2.5.

This is why monitor placement matters.

Reason 3: Sensors Can Respond at Different Speeds

Different monitors can have different response characteristics.

Imagine cooking causes PM2.5 to rise rapidly.

Monitor A may react slightly earlier.

Monitor B may respond differently.

A few moments later, both may show the same general trend.

If you only compare them during the transition, the difference may appear larger.

This is why:

Trend comparison is often more informative than one-second comparison.

Reason 4: Internal Algorithms Can Differ

Consumer air-quality devices may process sensor signals differently.

Manufacturers can use different methods for:

signal processing

averaging

display updating

and

AQI presentation.

Therefore, two devices using different sensing systems do not necessarily display identical values at every moment.

Reason 5: One Device Is Inside an Air Purifier

This is especially important.

Many air purifiers have built-in PM2.5 sensors.

But where is that sensor?

Inside or near the purifier.

The Temtop S1+ can be positioned elsewhere in the room.

For example:

Purifier Sensor

Near the purifier's air intake.

S1+

Near the occupied area.

These are different sampling locations.

You should not automatically expect perfect agreement.

Purifier Reading vs Independent Monitor

Imagine the purifier sits in one corner.

The S1+ sits near the centre of the room.

The purifier display says:

PM2.5 = 8

while S1+ says:

PM2.5 = 13.

Before deciding something is wrong, ask:

Are they measuring exactly the same air?

Usually, they are not.

That is one reason an independent monitor can be useful.

It gives you another measurement point.

Don't Put S1+ at the Purifier Clean-Air Outlet

This is one of the most common testing mistakes.

If you place S1+ directly beside the purifier outlet, it may disproportionately sample recently filtered air.

The reading may therefore be lower than conditions elsewhere in the room.

For general room monitoring:

Place the S1+ in a representative occupied location away from the immediate purifier outlet.

Direct Air-Conditioner Airflow Can Also Affect Measurement

Avoid placing the monitor directly under or immediately in front of an air-conditioner discharge.

Strong airflow can create a local measurement environment that may not represent the rest of the room.

The same applies to:

Standing fans

Ceiling-fan airflow

and

strong cross ventilation.

Ask:

“Is this position representative of the environment I want to understand?”

Window Placement Can Create Another Extreme

Suppose the S1+ is placed directly beside an open window during haze.

It may strongly respond to incoming outdoor air.

That can be useful if your specific question is:

“What is entering through this window?”

But it is not necessarily the best position for:

general bedroom PM2.5.

Measurement location should match the objective.

There Is No Single “Perfect” Monitor Location

The correct position depends on your question.

For General Room PM2.5

Use a representative occupied area.

For Purifier Testing

Keep the monitor away from the immediate clean-air outlet.

For Window Investigation

Use a consistent indoor position and observe before/after changes.

For Cooking Impact

Measure in the occupied living/dining area rather than directly above the stove.

Measurement objective determines placement.

Why Does My S1+ Reading Keep Moving?

PM2.5 is dynamic.

Particles:

enter

move

settle

become airborne again

are generated

and

are filtered.

Therefore, a PM2.5 monitor should not be expected to behave like a static thermometer in a perfectly stable environment.

Small fluctuations are normal.

Don't Expect a Perfectly Flat Number

Some users become concerned when they see:

8.1

↓

8.7

↓

8.3

↓

9.0

↓

8.5

This does not automatically indicate a problem.

Indoor particulate concentration changes continuously.

The more useful question is whether there is a meaningful trend.

For example:

↓

immediately after a household activity is much more significant than tiny normal fluctuations.

Trend Matters More Than Noise

This principle is extremely useful:

Don't chase every decimal.

Look for:

Large increases

Sustained increases

Consistent decreases

Repeatable patterns

and

responses to actions.

That is where a PM2.5 monitor provides real household value.

A Better Way to Test Your S1+

Instead of comparing it against another monitor for ten seconds, perform environmental response tests.

For example:

Test 1 — Stable Room

Leave S1+ in one location and observe the baseline.

Test 2 — Normal Cooking Event

Keep S1+ in the living/dining area and observe whether PM2.5 responds.

Test 3 — Purifier

Switch on the purifier and observe whether PM2.5 trends downward.

Test 4 — Different Day

Repeat under similar conditions.

You are looking for:

consistent environmental response.

Repeatability Is Valuable

Suppose:

Monday

Cooking causes PM2.5 to rise.

Tuesday

Cooking causes a similar rise.

Wednesday

Cooking again produces a noticeable increase.

Then:

Purifier operation repeatedly reduces PM2.5 afterward.

This repeated pattern provides useful evidence that the monitor is responding meaningfully to environmental changes.

How to Compare Two PM2.5 Monitors More Fairly

If you want to compare two devices:

1. Put Them Close Together

But do not block either air inlet.

2. Keep Them Away from Direct Airflow

Avoid purifier outlets, AC discharge and open windows.

3. Leave Them in a Stable Environment

Do not constantly move them.

4. Observe Over Time

Do not judge from one instant.

5. Create a Normal Environmental Change

For example, observe the natural effect of normal household cooking or purifier operation.

6. Compare the Trend

Do both respond in the same general direction?

This is more informative than asking:

“Why is one 12.3 and the other 13.8?”

Never Deliberately Create Heavy Smoke Just to Test the Sensor

There is no need to create unnecessary indoor pollution simply to see whether the PM2.5 number increases.

Use normal household environmental changes.

For example:

Normal cooking

Normal window use

Existing haze conditions

air purifier operation.

The purpose is to understand your environment—not create additional pollution.

Why Temperature and Humidity Accuracy Look Different

Unlike the PM2.5 accuracy figure, Temtop provides clear specified accuracy values for S1+ temperature and humidity.

Temperature:

Specified accuracy: ±0.5°C

Relative humidity:

Specified accuracy: ±3% RH

This is another reason not to invent a PM2.5 accuracy value simply because other specifications are available.

Each parameter has its own specification.

Temperature Can Differ Between Two Devices Too

Put two thermometers in different parts of an air-conditioned bedroom and they may not show exactly the same temperature.

Why?

Because one may be:

closer to AC airflow

while another is:

near a wall or furniture.

The same principle applies to air-quality measurements.

Location matters.

Humidity Can Vary by Position and Conditions

Relative humidity is influenced by temperature and local environmental conditions.

Therefore, if S1+ and another device are placed in different locations, small differences should not automatically be interpreted as instrument failure.

Always compare under controlled, reasonably similar conditions.

What About AQI Differences?

Another common question is:

“Why does one app show one AQI and another monitor show something different?”

AQI is an interpreted index.

Different systems or regions can use different pollutant breakpoints, averaging periods or presentation frameworks.

Therefore:

AQI numbers from different systems should not always be assumed to be directly interchangeable.

When comparing PM2.5 monitors, focus first on the underlying pollutant measurement and trend.

PM2.5 and AQI Are Not Exactly the Same Thing

PM2.5 is a measured particulate concentration.

AQI is an index used to communicate air-quality conditions.

Think of it this way:

PM2.5 = Measurement

AQI = Interpretation Framework

This distinction helps prevent confusion when different apps display different AQI values.

Can I Compare S1+ with Malaysia Outdoor Air Quality Data?

You can compare trends for context, but remember:

Outdoor monitoring station

and

your indoor S1+

are measuring different environments.

The outdoor station may be kilometres away.

Your S1+ may be:

inside a bedroom

behind closed windows

with an air purifier running.

Their readings are not expected to be identical.

The useful comparison is:

What happened outside, and how did my indoor environment respond?

Example: Malaysia Haze Day

Suppose outdoor particulate conditions worsen during the afternoon.

Your indoor S1+ shows:

Morning — lower PM2.5

Afternoon — gradual increase

Purifier ON — decline

This gives you useful information.

You have learned that:

outdoor conditions changed

and

your indoor room responded

and

filtration affected the indoor trend.

That is more valuable than demanding that the indoor reading match an outdoor station exactly.

Can a Consumer PM2.5 Monitor Replace Professional Equipment?

No—not automatically.

The S1+ is best positioned for:

home monitoring

PM2.5 awareness

haze monitoring

air purifier checking

and

environmental trend observation.

Professional applications may require:

specific measurement methods

defined accuracy requirements

calibration

traceability

sampling procedures

and

professional-grade instrumentation.

Use the appropriate instrument for the application.

Consumer Monitoring and Compliance Testing Are Different

For example:

Homeowner Question

“Does my purifier reduce bedroom PM2.5?”

S1+ can be very useful.

Factory Compliance Question

“Does this workplace meet a specific regulatory exposure requirement?”

That is a different type of measurement problem.

Do not treat them as equivalent.

Is S1+ Useful If It Is Not a Laboratory Instrument?

Yes.

A device does not need to be a laboratory instrument to provide useful household information.

Consider what most home users actually want to know:

Is PM2.5 rising?

Is haze entering the room?

Does cooking create a spike?

Does the purifier bring PM2.5 down?

Which room has higher PM2.5?

What happens over time?

These are trend and environmental-awareness questions.

That is where S1+ fits.

Think Like an Instrument User

A useful measurement is not just:

Sensor + Number

It is:

Sensor + Correct Placement + Context + Trend + Interpretation

Even an excellent instrument can produce misleading conclusions if it is used in the wrong location.

Good measurement practice matters.

Common PM2.5 Monitor Mistakes

Mistake 1 — Expecting Two Devices to Match Exactly

Different sensors and locations can produce differences.

Mistake 2 — Comparing Different Locations

Bedroom monitor vs living-room purifier is not a fair direct comparison.

Mistake 3 — Putting S1+ Beside Purifier Outlet

This may not represent the whole room.

Mistake 4 — Testing Beside an Open Window

Unless window infiltration is specifically what you want to investigate.

Mistake 5 — Moving the Monitor Constantly

This destroys consistency.

Mistake 6 — Obsessing Over Tiny Fluctuations

Look for meaningful trends.

Mistake 7 — Assuming Resolution Equals Accuracy

It does not.

Mistake 8 — Assuming PM2.5 Measures Everything

It does not measure CO₂, HCHO or TVOC.

What S1+ Does Not Measure

The Temtop S1+ does not measure:

CO₂

HCHO / Formaldehyde

TVOC

Therefore:

Low PM2.5 does not prove good ventilation.

Low PM2.5 does not prove low formaldehyde.

Low PM2.5 does not prove low TVOC.

Different pollutants require different sensors.

Which Temtop Should You Choose?

Temtop S1+

Best aligned with:

PM2.5

Haze

Air Purifier Checking

Temperature

Humidity

Home Trend Monitoring

Temtop M10i

Consider when your measurement objective also includes:

HCHO

and

TVOC.

Temtop M2000 2nd

Consider when broader indoor-air monitoring including:

CO₂

is required.

Define the question first. Choose the instrument second.

Frequently Asked Questions

Is Temtop S1+ accurate?

The S1+ is designed as a consumer indoor environmental monitor using laser particulate sensing for PM2.5 monitoring. For household use, focus on correct placement, meaningful trends and repeatable environmental response rather than expecting perfect numerical agreement with every other device.

What is the PM2.5 accuracy of Temtop S1+?

Do not infer accuracy from its 0.1 μg/m³ resolution. Resolution and accuracy are different specifications. Use current official Temtop documentation for any formal accuracy requirement.

Why does S1+ show a different PM2.5 reading from my air purifier?

The devices may use different sensors, processing methods and measurement locations. Your purifier measures near its own sensor, while S1+ may be elsewhere in the room.

Why do two PM2.5 monitors show different readings?

Sensor characteristics, airflow, placement, response behaviour and changing particle concentration can all contribute.

Should I put S1+ beside my air purifier to compare them?

Not if your objective is representative room monitoring. Keep S1+ away from the immediate clean-air outlet.

Why does the PM2.5 number keep changing?

Indoor particulate concentration is dynamic. Small fluctuations are normal; focus on meaningful trends and repeatable patterns.

Is 0.1 μg/m³ resolution the same as ±0.1 μg/m³ accuracy?

No. Resolution and accuracy are different concepts.

Can I compare S1+ directly with outdoor Malaysia AQI?

Use outdoor data as context, but remember that outdoor monitoring stations and your indoor S1+ measure different locations and environments.

Can S1+ be used for regulatory compliance testing?

It should not automatically be treated as a professional compliance instrument. Formal assessments may require specified equipment, procedures, calibration and applicable standards.

Don't Ask Only “Is This Number Exactly Right?”

A better question is:

“Is the monitor helping me understand what is happening in my room?”

When cooking begins:

Does PM2.5 respond?

When outdoor haze worsens:

Does the indoor trend change?

When the purifier starts:

Does PM2.5 decline?

When you move from living room to bedroom:

Do the environmental conditions differ?

When the same activity happens again:

Does a similar pattern appear?

That is how a household PM2.5 monitor becomes useful.

The Temtop S1+ provides:

PM2.5 + AQI + Temperature + Relative Humidity

with BLE app connectivity for trend monitoring.

Its value is not found by staring at one decimal place and comparing it against another device every second.

Its value comes from:

Correct Placement

Consistent Measurement

Trend Observation

Environmental Context

Repeatable Patterns

The principle is simple:

Don't judge a PM2.5 monitor from one number.

Judge what the measurements teach you about your environment.

Contact MTM Precision

MTM Precision Sdn. Bhd.

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia

🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: 016-660 7346

For enquiries about Temtop S1+, PM2.5 monitors, indoor air quality monitors and environmental monitoring instruments in Malaysia, contact MTM Precision.

Serving customers throughout Selangor, Kuala Lumpur, Johor, Penang, Perak, Melaka, Negeri Sembilan, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sarawak and Sabah.