Ultrasonic Sound Beam Burglar Alarm
This one-of-a-kind ultrasonic burglar alarm makes use of an inaudible and invisible sound beam produced by ultrasonic waves to detect any movement. When pushed at a frequency of 40 kHz, u…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Ultrasonic Sound Beam Burglar Alarm is a electronics project. This one-of-a-kind ultrasonic burglar alarm makes use of an inaudible and invisible sound beam produced by ultrasonic waves to detect any movement. When pushed at a frequency of 40 kHz, u…
- Source pages
- 157-159
- Named parts
- 6
- Build goal
- Working, tested prototype
Tools you need
- Digital multimeter
- Wire stripper and side cutters
- Soldering iron with a fine tip
- Current-limited bench supply
Use eye protection, good lighting, and a clean insulated surface throughout the build.
Safety precautions
- Disconnect every power source before changing a connection.
- Check component polarity, pinout, and supply voltage twice.
- Use a current limit for the first power-up.
- This project may involve hazardous voltage. Work only with qualified supervision and proper isolation.
Gather, identify, and understand every part.
Use the standardized inventory, then open What's this? to learn each part's role, advantages, limitations, handling, and specifications.
What's this?Image, role, pros, cons, handling & specifications
Buzzer
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for Buzzer; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
Power supply
A power component supplies, converts, stores, or regulates energy for the project.
What it does hereIt must provide the documented voltage, polarity, isolation, and sufficient current safely.
Buy / compare this part ↗Advantages
- Stable power improves reliability
- Current limiting protects first tests
- Regulation reduces resets and noise
Limitations
- Wrong polarity can cause immediate damage
- Underrated parts overheat
- Mains circuits require qualified supervision
Handling
- Measure output before connection
- Use a fuse or current limit
- Insulate exposed conductors
Specifications to verify
- Use the exact model, value, package, and rating listed for Power supply; similar-looking parts are not always interchangeable.
- Confirm input/output voltage, current, polarity, connector, isolation, and thermal rating.
What's this?Image, role, pros, cons, handling & specifications
CD4001
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for CD4001; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
T4, T5 - transistor stages identified in the circuit
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for T4, T5 - transistor stages identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
LED1 - indicator LED identified in the circuit
An output component turns an electrical control signal into light, sound, motion, switching, or displayed information.
What it does hereIt presents the circuit result or acts on the physical world.
Buy / compare this part ↗Advantages
- Makes system state visible
- Can be tested separately
- Supports clear troubleshooting
Limitations
- Loads may exceed controller current
- Polarity or driver direction can matter
- Inductive loads create voltage spikes
Handling
- Use the documented driver stage
- Check polarity and load current
- Add flyback protection for inductive loads
Specifications to verify
- Use the exact model, value, package, and rating listed for LED1 - indicator LED identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm voltage, current, polarity, interface, driver requirements, and duty cycle.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWVR1, VR2 - preset potentiometers identified in the circuit
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for VR1, VR2 - preset potentiometers identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
Connect one verified path at a time.
Explore the named components and standardized signal flow, then use Source Check to verify exact physical pins, values, and topology before applying power.
Trace this circuit.
Ultrasonic Sound Beam Burglar Alarm: interactive parts, standardized terminals, responsive anchored wires, student explanations, and the original circuit reference in one shared system.
Trace before wiring
Follow power, ground, inputs, processing, and outputs in that order. Never guess a pin from package shape alone.
Connect with power off
Make short, labelled connections and share a common ground only where the schematic requires it.
Inspect every joint
Check continuity, polarity, adjacent shorts, and loose connections before the first power-up.
Open all source diagrams and build views 2 visuals
Confirm the hardware-only control path.
This project does not include firmware in the source. The circuit itself provides the required behaviour.
How to connect
- Match every controller label to the circuit view and source pin map.
- Join grounds before signal wires when separate low-voltage supplies are used.
- Keep motors, relays, pumps, and other loads on a suitable driver and external supply.
Common mistakes
Reversed VCC/GND, board-label versus GPIO-number confusion, missing common ground, and charge-only USB cables.
Troubleshoot
Disconnect loads, continuity-test one path at a time, then test with a current limit.
Software preparation
No IDE, board package, library, or firmware upload is required for this project.
If you add a programmable controller as an extension, document its pin map separately.
How to upload code
The original design is implemented entirely in hardware, so proceed after verifying the circuit and supply.
Assemble, deploy, test, and troubleshoot.
Use the complete source notes in build order, then pass the final checks before calling the project finished.
Build in functional stages
- Power and regulation
- Controller or processing stage
- Inputs and sensors
- Outputs and loads
- Enclosure and strain relief
Power up safely
- Inspect unpowered continuity first
- Apply the lowest safe current limit
- Measure supply rails before signals
- Add one load at a time
- Record expected and actual results
Work from simple to complex
- Confirm power, ground, polarity, and orientation
- Compare each pin with the source
- Test inputs separately from outputs
- Replace only one variable at a time
- Power off before every correction
Follow the documented instructions.
These notes come from this project's source and remain in their original order.
Project overview
Project build noteThis one-of-a-kind ultrasonic burglar alarm makes use of an inaudible and invisible sound beam produced by ultrasonic waves to detect any movement. When pushed at a frequency of 40 kHz, ultrasonic transducers are able to function at their most effective level. Therefore, the buzzer and the relay are both controlled by an ultrasonic transmitter and receiver pair that operates at a frequency of 40 kHz. Fig. 1: Ultrasonic Burglar Alarm: Transmitter unit The CMOS IC CD4001 serves as the focal point of the transmitter unit's construction (see Fig. 1). The oscillator frequency can be changed to roughly 40 kHz by setting the 22-kilo-ohm preset (VR1) on the variable resistor 1. The current drain of the ultrasonic transmitter transducer is extremely low, and it is driven by two complimentary buffer stages of CD4001 components.
Fig2. Ultrasonic Burglar Alarm: Receiver circuit A two-stage 40 kHz preamplifier is utilized by the receiver unit, which is then followed by a switching circuit, buzzer driver, and other components (see Fig. 2). Make the necessary adjustments to the value of VR2 inside the receiver's circuit so that the buzzer will no longer ring while the receiver is picking up ultrasonic sound from the transmitter. When the ultrasonic beam is disrupted, either by the movement of a person or any other object that crosses its path, the npn transistor T4 stops conducting, and the transistor T5 begins conducting instead. It turns on the buzzer as well as LED1 for approximately three to four seconds. This duration is dependent on the amount of time it takes for the 470 F capacitor (C8) that is connected at the base of transistor T5 to discharge completely through the resistor R13. By adjusting the values of C8 and R13, the appropriate length of time for the burglar alarm to sound can be selected.
Construction & Testing
Project build noteA power supply that is controlled between 9-12 volts is used to power the alarm circuit, which consists of a transmitter, a receiver, and other connected circuits. The circuit for the receiver needs a controlled 12V supply. You are also free to use a power supply that is not controlled here. On separate PCBs designed for general use, assemble the circuits for the transmitter and the receiver. Adjust the positioning of the ultrasonic transducer so that the signal will reach the ultrasonic receiver unobstructed.
A relay can take the place of the piezobuzzer (PZ1) as the controller of the alarm that is powered by the mains.
You built Ultrasonic Sound Beam Burglar Alarm.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
Sunset Lamp
Ready to reuse what you learned in another project from the same track?
Start this project →