Motorbike Alarm
This alarm is easy to make and can be put on bikes to keep them from being stolen. The tiny circuit doesn't have any complicated wiring, so it can be hidden anywhere. Almost any bike can…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Motorbike Alarm is a electronics project. This alarm is easy to make and can be put on bikes to keep them from being stolen. The tiny circuit doesn't have any complicated wiring, so it can be hidden anywhere. Almost any bike can…
- Source pages
- 548-551
- Named parts
- 1
- 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.
- Keep liquids, loose metal, and uninsulated wires away from the bench.
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
T1, T2, T3, T4 - 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 T1, T2, T3, T4 - 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.
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.
Motorbike 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 1 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 alarm is easy to make and can be put on bikes to keep them from being stolen. The tiny circuit doesn't have any complicated wiring, so it can be hidden anywhere. Almost any bike can use it as long as it has a battery. The standby current is zero, so it doesn't drain the battery.
The hidden switch S1 can be a small push-to-on switch, a reed switch with a magnet, or any other simple device that works the same way. The circuit is built around two low-voltage MOSFETs that have been set up as monostable timers. Key S2 is an ignition switch on a motorcycle, and switch S3 is a tilt switch. When the motorbike key S2 is turned on, it sends power to the gate of MOSFET T2. When you use key S2 to turn off the bike's ignition, you have about 15 seconds to get off. This is done by resistor R6 to discharge capacitor C3. After that, if someone tries to get on the bike or move it, the alarm goes off for about 15 seconds and the ignition circuit is cut. During parking, the hidden switch S1 is usually open, so it doesn't let the mosfet T1 turn on. But when someone starts the bike with the ignition switch S2, diode D1 and resistor R5 turn on MOSFET T2. When relay RL1 (12V, 2C/O) is turned on, the alarm (built around IC1) goes off and the ignition coil is taken out of the circuit. When the ignition coil is
disconnected, the spark plug can't make a spark. Usually, there is a wire going from the alternator to the ignition coil. This wire has to go through one of the N/C1 contacts of relay RL1, as shown in Figure. Also, when the coil is disconnected, power is sent to the sound generator IC UM3561 (IC1) through the N/O2 contact of relay RL1. This turns on the T3 and T4 Darlington pair, which makes the siren sound through loudspeaker LS1. To start the car, you need to turn on both the hidden switch S1 and the ignition key S2. If you don't, the alarm will go off. When S1 is turned on, SCR1 is set off, which sets off MOSFET T1. MOSFET T1 is set up so that it stops MOSFET T2 from working. So, MOSFET T2 doesn't turn on, relay RL1 stays off, the alarm stays off, and the ignition coil stays connected to the circuit. When the spark plug is connected to the ignition coil, the spark plug is better able to make a spark. The bike can't be stolen if the owner is the only one who can use the hidden switch S1. With the S3 tilt switch, you can't move the vehicle without turning it on. Versions of the switch made of glass and metal don't bounce and break quickly, even when tilted slowly. Unless otherwise stated, the angle at which the switch must be tilted for the contacts to work (the "operating angle") must be about 1.5 to 2 times the angle given for the "difference." The differential angle is the difference between where the door is "just closed" and where it is "just open." The tilt switch has features like contacts that make and break when the switch is shaken, contacts that go back to the open position when the switch is still, non-position sensitivity, inert gas and hermetic sealing to protect the contacts, and a steel housing that is tin-plated. If you can't get the tilt switch, you can use a reed switch (N/O) and a piece of magnet to replace it.
The magnet and reed switch should be set up so that the switch contacts close when the bike stand is moved from its resting position.
You built Motorbike Alarm.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
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