Gas Alert Alarm School Project & Demonstration kit Using MQ135 Gas Sensor

Pre-Wired Relay-Based School Project & Demonstration Kit

See gas sensing, threshold response and automatic alert switching come to life.

Turn gas-sensor technology, semiconductor behaviour and relay-controlled alert systems into a live, observable learning experience.

The Go Science Classroom Series Gas Alert Alarm brings an MQ135 gas sensor module, adjustable comparator circuit, 5V relay module, active buzzer and reverse-polarity protection diode together on one complete pre-wired working platform.

During a carefully supervised demonstration, the MQ135 sensor responds to the presence of suitable gas or vapour near its sensing surface. When the sensor response crosses the selected threshold, its digital output activates the relay. The relay switches the buzzer circuit and produces a clear audible alert.

Students can follow the complete functional sequence:

Sense the Air → Compare the Response → Trigger the Relay → Sound the Alert

The model provides a practical foundation for exploring gas sensing, sensor circuits, adjustable thresholds, semiconductor technology, electromagnetic relay switching, audible alerts and home-safety awareness concepts.

Designed for Grades 7–12, it is suitable for school projects, science exhibitions, classroom demonstrations, basic electronics learning and sensor-based safety presentations.

A Complete Guided Learning Experience

Working model, illustrated manual and video demonstration—all connected.

Every Go Science Classroom Series kit is supported by a guided learning experience that helps students understand the concept, prepare the demonstration and confidently explain the complete system.

This kit includes access to:

• A detailed full-colour digital instruction manual
• Illustrated component explanations
• Step-by-step demonstration guidance
• A dedicated video demonstration
• QR access to digital learning resources
• Safety, care and troubleshooting information
• Concept recap and Certificate of Completion

The learning journey is designed to take students through:

Explore → Understand → Watch → Prepare → Observe → Explain → Complete

Students can first study the working principle through the manual, watch the actual model in the demonstration video and then use both resources while preparing for a school project, classroom presentation or science exhibition.

What’s in the Kit?

• MQ135 gas-sensor module
• Adjustable comparator circuit
• 5V relay/control module
• 5V active buzzer
• Inline reverse-polarity protection diode
• House display model
• Wooden component-support stand
• Decorative artificial-grass base
• Pre-wired electrical connections
• Battery snap connector
• Ready-to-use educational working model
• QR access to the detailed digital manual
• Detailed 16-page full-colour digital instruction manual
• QR access to the video demonstration from the kit box
• Step-by-step video demonstration
• Illustrated component explanations
• Working-principle guidance
• Safety, care and troubleshooting support
• Concept recap and Certificate of Completion

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Required Separately

9V Battery

The model requires one fresh 9V battery.

Battery is not included.

Supervised Demonstration Source

The supervised demonstration shown in the supplied manual and video uses a small, brief release from an unlit gas lighter.

Gas lighter is not included.

Only an adult or teacher may conduct this part of the activity. The lighter must never be ignited, and the demonstration must take place in a well-ventilated environment completely free from flames, sparks, hot surfaces and flammable materials.

Product Specifications

The product manual and packaging confirm the MQ135 sensor, relay, buzzer, protection diode, battery requirement, dimensions and educational-use limitations.

Detailed Full-Colour Digital Manual Included

Scan, explore and demonstrate with confidence.

A QR code provided with the kit gives students access to a dedicated digital instruction and learning manual created specifically for the MQ135 Gas Alert Alarm model.

The manual can be opened on a phone, tablet or computer and revisited during:

• Project preparation
• Component identification
• Classroom learning
• Demonstration setup
• Science-exhibition practice
• Project-report writing
• Viva preparation
• Troubleshooting
• Revision and concept recap

The current manual contains 16 colourful illustrated pages covering the complete learning journey.

It includes:

• An introduction to the gas-alert concept
• A visual guide to the included components
• MQ135 gas-sensor explanation
• Relay-module and protection-diode concepts
• The complete detection-to-alert sequence
• Illustrated setup and operating guidance
• Sensor warm-up and threshold-response information
• Supervised demonstration guidance
• Troubleshooting support
• Safe shutdown, care and storage instructions
• Concept recap
• Printable Certificate of Completion

The component guide appears on pages 5–6, the complete working sequence on page 7, setup and supervised testing guidance on pages 8–10, troubleshooting on page 11, storage guidance on page 12, concept recap on page 13 and the completion certificate on page 15.

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Step-by-Step Video Demonstration Included

Watch the actual model before conducting the demonstration.

Every kit also provides access to a dedicated video showing the physical model, its components and its working sequence.

The supplied video demonstrates:

• The complete product and box
• The contextual house model
• The MQ135 sensor module
• The relay and buzzer circuit
• The pre-wired connections
• The battery connection
• The sensor-response demonstration
• Relay activation
• Audible buzzer output
• Safe completion of the activity

The video is available through three convenient access points:

Product Gallery

The demonstration video is included alongside the product images on the Go Science product page, allowing parents, teachers and students to view the model before purchase.

Go Science YouTube Channel

The video is also published through the official Go Science YouTube presence for convenient viewing, sharing and revision.

QR Code on the Kit Box

A QR code on the side of the product box provides quick access to the demonstration video whenever students need to revisit the setup or working sequence.

This creates a continuous guided experience:

Scan → Watch → Prepare → Demonstrate → Rewatch

Internet access and a compatible QR-scanning device are required to open the online resources.

From Gas Presence to Audible Alert

Explore how sensing, comparison and switching work together.

The model presents gas detection as a connected electronic system.

The MQ135 module responds to changes around its heated semiconductor sensing element. Its onboard comparator evaluates the response against the threshold selected using the adjustment control.

When the response crosses the selected threshold, the module changes its digital output state. This output activates the relay module, which switches the buzzer circuit and produces an audible alert.

Students can trace the complete pathway:

Surrounding Air → MQ135 Sensor → Comparator → Digital Signal → Relay → Buzzer

Each stage performs a specific function, allowing students to understand how several electronic components coordinate to produce an automatic response.

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Pre-Wired for Direct Exploration

Begin with a complete working foundation.

The MQ135 sensor, relay module, buzzer, protection diode, battery connector and interconnecting wires are arranged as one pre-wired working system.

This allows students to move directly into meaningful exploration:

• Identify the function of each component
• Observe the sensor’s warm-up behaviour
• Understand threshold-based detection
• Follow the digital signal from sensor to relay
• Hear the relay’s mechanical switching response
• Observe the buzzer alert
• Conduct repeated supervised demonstrations
• Compare clean-air and test conditions
• Record and explain observations
• Investigate threshold adjustment
• Troubleshoot changes in system behaviour
• Connect the model with wider sensor and automation concepts

The model is designed to be:

Observed → Tested → Retested → Understood → Explained → Built Upon

Watch the Complete System Respond

1. Power the Model

Connect a fresh 9V battery using the supplied battery snap connector.

The sensor module receives power and its onboard heating element begins stabilising.

2. Allow the Sensor to Stabilise

The MQ135 sensor requires a brief warm-up period before the classroom demonstration.

During this time, its internal sensing element begins reaching a more stable operating condition.

3. Monitor the Surrounding Air

The MQ135 module acts as the system input.

It responds to changes in the gas or vapour conditions close to its sensing mesh.

4. Compare the Response

The module’s onboard comparator evaluates the sensor response against the selected sensitivity threshold.

5. Trigger the Relay

When the response crosses the threshold, the module’s digital output sends a trigger to the 5V relay module.

Students may hear the relay produce a distinct mechanical click.

6. Sound the Alert

The relay completes the buzzer circuit.

The active buzzer produces a clear audible alert representing the output of the system.

7. Reset

When the test vapour disperses into fresh air and the sensor response moves below the threshold, the relay releases and the buzzer stops.

The complete functional sequence is:

Gas or Vapour Detected → Threshold Crossed → Relay Activated → Buzzer Alert

The supplied technical manual confirms the use of the MQ135 module, adjustable comparator, relay switching stage, active buzzer and protection diode.

Explore the MQ135 Gas Sensor

Observe how a semiconductor sensor responds to its surroundings.

The MQ135 module contains a heated sensing element based on a tin-dioxide semiconductor material.

Its electrical behaviour changes when it is exposed to certain gases and vapours. The sensor module converts this change into an electronic response that can be evaluated by its comparator circuit.

The MQ135 is commonly responsive to several substances, which may include:

• Ammonia
• Alcohol vapour
• Benzene-related vapours
• Smoke
• Nitrogen-oxide-related gases
• Carbon-dioxide-related changes

The response is broad and may be influenced by several gases, vapours and environmental conditions. The model therefore demonstrates general threshold-based gas sensing rather than identifying a particular gas with certainty.

Students can explore:

• Semiconductor gas sensing
• Heated sensor elements
• Electrical conductivity changes
• Sensor response
• Gas and vapour presence
• Environmental inputs
• Signal conditioning
• Cause-and-effect relationships
• How changing surroundings can create an electronic output

The model does not display gas concentration, parts per million, AQI or the identity of a detected gas.

Discover Threshold-Based Detection

See how an adjustable setting creates a trigger point.

The onboard comparator checks the changing sensor response against a selected threshold.

This introduces an important electronic concept: a sensor may produce a continuously changing response, while a comparator determines when that response has crossed a chosen trigger level.

Students can observe:

• The sensor producing the initial response
• The comparator evaluating that response
• The sensitivity control influencing the trigger point
• The digital output changing state
• The relay receiving the trigger
• The buzzer responding to the threshold event

Under adult or teacher guidance, small threshold adjustments may be used to explore:

• Why the buzzer may activate too easily
• Why the sensor may require fresh air before resetting
• How sensitivity influences the response
• Why ambient conditions can affect sensing
• Why only one adjustment should be changed at a time
• How the model can be reset and tested again

This is a threshold demonstration, not a calibrated measurement instrument.

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Explore Relay-Based Switching

Hear an electrical signal become a physical switching action.

The model includes a 5V relay module between the sensor output and the buzzer circuit.

When the MQ135 module produces the trigger signal, the relay’s internal electromagnetic coil activates. Its contacts change position and complete the buzzer circuit.

Students can explore:

• Electromagnetic relays
• Relay coils
• Common, Normally Open and Normally Closed contacts
• Electrically controlled switching
• Mechanical switching action
• Sensor-controlled outputs
• Input, control and output stages
• How one circuit can control another circuit
• Automatic response systems

The relay’s indicator and mechanical click provide visible and audible evidence that the switching stage has activated.

Reverse-Polarity Protection

Explore how a diode helps protect an electronic system.

The model includes an inline protection diode between the battery connection and the electronic circuit.

A diode allows current to flow primarily in one direction. If the battery is accidentally connected with reversed polarity, the diode helps block the incorrect current path and protect the sensitive circuit components.

Students can explore:

• Positive and negative polarity
• Direction of current flow
• Diode behaviour
• Reverse-polarity protection
• Circuit-protection design
• Why electronic components require correct battery orientation

The diode provides an additional protective feature. The battery must still always be connected carefully and in the correct orientation.

Understand the Complete Functional System

A Home-Safety Context Students Can Understand

Connect sensor technology with a recognisable application.

The house-based model gives the electronics a clear context.

Each element represents a stage within a gas-alert concept:

• The house model represents the area being monitored.
• The MQ135 sensor represents the detection stage.
• The comparator represents the decision threshold.
• The relay represents the automatic switching stage.
• The buzzer represents the audible warning output.
• The battery powers the demonstration.
• The protection diode represents circuit protection.

This arrangement helps students explain not only what each component is, but also:

• Why it is present
• What information it receives
• What decision or action it performs
• How it connects with the next stage
• How all stages work together as one automatic system

The house layout creates a home-safety awareness context. It does not make the product a real home-protection device.

Test. Observe. Discover.

All demonstrations must be performed only by an adult or teacher in a well-ventilated area, away from flames, sparks, heat and flammable materials.

Clean-Air Baseline Observation

Power the model and allow the sensor to stabilise.

Observe whether:

• The power indicator is illuminated
• The relay remains inactive
• The buzzer remains silent
• The module reaches a stable condition

Threshold-Response Observation

Under adult or teacher control, expose the sensor briefly to the approved demonstration condition shown in the manual and video.

Observe the sequence:

1. Sensor response changes
2. Comparator threshold is crossed
3. Relay activates
4. Relay produces a mechanical click
5. Buzzer sounds
6. Test source is removed
7. Gas or vapour disperses
8. Relay releases
9. Buzzer stops

Repeatability Test

After the sensor returns to its normal state, repeat the supervised demonstration.

Record whether the same functional sequence occurs.

Response-and-Recovery Observation

Observe both stages:

• How the system reacts when the test condition is introduced
• How the system resets after the surrounding air clears

Sensitivity Exploration

Under teacher guidance, make a very small adjustment to the onboard potentiometer.

Repeat the observation and compare how the trigger behaviour changes.

Only small controlled adjustments should be made, and the original position should be noted.

Signal-Path Investigation

Students can identify and trace:

• Sensor input
• Comparator stage
• Digital-output wire
• Relay input
• Relay switching contacts
• Buzzer circuit
• Battery supply
• Protection diode

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Learn Through Every Demonstration

Watch

Review the complete video before beginning.

Predict

Will the buzzer activate when the sensor response crosses the threshold?

Prepare

Place the model in a safe and well-ventilated demonstration area.

Observe

Watch the indicators, listen for the relay click and hear the buzzer response.

Record

Document the sensor condition, threshold setting and output response.

Compare

Compare the normal-air condition with the supervised test condition.

Analyse

Explain why the relay activated or why the system remained silent.

Troubleshoot

Check the battery, sensor warm-up, surrounding air, sensitivity control and visible connections.

Explain

Describe the complete sensor-to-alert pathway.

Extend

Develop further questions about air-quality monitoring, gas sensors, relay circuits and automatic alert systems.

Explore Key Concepts

Gas-Sensor Technology

• MQ135 gas sensor
• Semiconductor sensing
• Tin-dioxide sensing element
• Sensor heating
• Gas and vapour response
• Environmental inputs

Electronic Circuits

• Power supply
• Comparator circuits
• Adjustable thresholds
• Digital output
• Open and completed circuits
• Audible output devices

Relay Switching

• Electromagnetic coils
• Relay contacts
• Normally Open switching
• Signal-controlled circuits
• Automatic response
• Electrical isolation concepts

Circuit Protection

• Battery polarity
• Diodes
• One-directional current flow
• Reverse-polarity protection
• Component protection

Practical Investigation

• Warm-up observation
• Threshold response
• Repeatability
• Recovery time
• Cause-and-effect reasoning
• Troubleshooting

Safety Awareness

• Monitoring concepts
• Warning outputs
• Ventilation awareness
• Responsible demonstration practice
• Limitations of educational models

One Model. Multiple Learning Outcomes.

The model allows students to explore how:

• A semiconductor sensor responds to environmental changes
• A comparator checks the response against a threshold
• A digital signal controls a relay
• A relay switches a separate output circuit
• A buzzer communicates an alert
• A diode helps protect the power connection
• A sensor system can reset after conditions change
• Visible and audible responses support observation
• Several modules work together as one coordinated system
• Electronic sensing can be connected with safety-awareness concepts

Built for Confident Demonstration

The visible components, relay response, audible buzzer and guided learning resources make the model suitable for:

• School science projects
• Science exhibitions
• Classroom demonstrations
• Gas-sensor demonstrations
• Relay-switching demonstrations
• Semiconductor-electronics activities
• Home-safety awareness presentations
• Air-quality concept discussions
• Sensor-circuit explanations
• Threshold-response activities
• STEM learning
• Experiential learning
• Project-based learning
• Project-report preparation
• Viva and oral presentation
• Grades 7–12

Suggested Student Explanation

“This is an MQ135 gas-alert working model. The MQ135 sensor responds to changes in nearby gas or vapour conditions. Its comparator checks the sensor response against an adjustable threshold. When that threshold is crossed, the module sends a digital signal to the relay. The relay acts as an electrically controlled switch and completes the buzzer circuit. The buzzer then produces an audible alert. When the gas or vapour disperses, the relay releases and the buzzer stops. The model demonstrates semiconductor gas sensing, threshold comparison, relay switching and automatic alert systems.”

Build Upon the Foundation

Once students understand the original gas-sensing and alert sequence, the model can inspire further questions:

• Could an LED provide a visual alert?
• Could a display show the sensor’s analogue response?
• Could different threshold settings be compared?
• Could the sensor output be connected to a microcontroller?
• Could response events be recorded over time?
• Could more than one sensor be studied?
• Could a ventilation-fan concept be explored?
• Could a wireless notification concept be added?
• Could the project compare different environmental sensors?
• Could the model be expanded into a smart-building display?
• How would a calibrated instrument differ from this threshold model?
• Why are real safety systems tested and certified?

These are further learning directions. Additional components, circuit modifications and appropriate technical guidance may be required.

This Concept Can Also Be Used to Explore

The sensing, threshold, switching and alert sequence can support discussions around:

• Gas-presence alert concepts
• Air-quality monitoring concepts
• Smoke-response demonstrations
• Industrial air-monitoring concepts
• Laboratory vapour-warning concepts
• Smart-building sensor systems
• Ventilation-control concepts
• Sensor-controlled fan concepts
• Environmental monitoring
• Threshold-based warning circuits
• Relay-operated alarm systems
• Semiconductor-sensor projects
• Automatic notification concepts
• Multi-sensor safety systems
• Input-process-output systems
• Electronic automation

These are educational concept extensions based on the model’s functional sequence. They are not additional built-in features or claims of real-world protection

Curriculum and Concept Connections

The project can support classroom discussion around:

• Electrical circuits
• Magnetic effects of electric current
• Electromagnetic relay operation
• Semiconductor electronics
• Environmental awareness
• Air-quality concepts
• Sensor technology
• Automatic warning systems
• Input-process-output relationships

The supplied concept-mapping document connects the model with selected electricity, electromagnetism, environment and semiconductor concepts for Grades 7–12. These are independent educational references and do not imply approval or endorsement by NCERT, CBSE or any school board.

A Complete Learning Journey

Scan the code.

Watch the demonstration.

Read the manual.

Power the model.

Allow the sensor to stabilise.

Observe the response.

Follow the signal.

Hear the relay switch.

Listen to the alert.

Record the result.

Explain the system.

Build upon the idea.

The Go Science MQ135 Gas Alert Alarm transforms semiconductor sensing, threshold comparison and relay-controlled alerts into a guided working experience students can observe, understand and confidently demonstrate.

Important Educational and Safety Information

This product is an educational demonstration model and science teaching aid.

• Adult or teacher supervision is mandatory for the gas demonstration.
• Use the model only in a well-ventilated area.
• Keep the demonstration area completely free from open flames.
• Keep away from sparks, hot surfaces and flammable materials.
• Never ignite the lighter during the demonstration.
• Release only the minimum brief amount required for observation.
• Never continuously discharge gas onto the sensor.
• Do not inhale gas or place the lighter near the face.
• Allow the sensor a brief warm-up period after power connection.
• Do not leave the model powered continuously.
• Keep the relay and buzzer activation brief.
• Connect the 9V battery using the correct orientation.
• Disconnect the battery immediately after every demonstration.
• Store the model in a cool, dry and ventilated location.
• Keep the sensor away from prolonged exposure to fumes, solvents and moisture.
• Internet access is required for the online manual and video.
• Product appearance, wire routing and component placement may vary slightly due to manufacturing and component availability.

Important Product Limitation

This product demonstrates a general threshold-based gas-sensor response.

It is not:

• A certified gas-leak detector
• A certified LPG detector
• A smoke alarm
• A carbon-monoxide detector
• A carbon-dioxide measuring instrument
• An AQI monitor
• A calibrated gas-concentration meter
• A home-security product
• An emergency-warning system
• A life-safety device
• A replacement for certified gas-detection equipment

It must never be relied upon to protect people, animals, buildings or property.

Return, Refund & Exchange Notice: This educational working model contains tested and sensitive electronic components. Kits that have been opened, powered, activated, tested, used, altered or exposed to gas, vapour, smoke, moisture or unsuitable operating conditions are not eligible for return, refund or exchange . Battery and demonstration lighter are not included. Please review the product description, included contents, dimensions, power requirement, demonstration video and safety instructions carefully before purchase.