The Truth About the OSS TEAM W01 Inductance Tester
If you’ve spent any time browsing electronics repair forums or watching diagnostic videos lately, you’ve probably seen it: A sleek, pen-sized black circuit board being waved over smartphone motherboards. The green LED lights up, and—boom—the component is declared healthy (claims many videos seen on Facebook and YouTube).

Advertisements call it a “Revolutionary Motherboard Repair Tool” that grants technicians “X-Ray Vision.” Sellers claim it can instantly stop the guesswork of component failures with a clear pass/fail signal.

But is the OSS TEAM W01 Inductance Tester truly a “secret weapon,” or is it just another over-hyped online hoax? Or something in between? Let’s strip away the marketing promises and look at what this tool actually does, how much it costs, and the hidden dangers you need to know about.

What is the OSS TEAM W01?
At its core, the OSS W01 is a compact, bare-board electromagnetic field (EMF) detector. It features:
A pointed detection tip at one end.
A central detection button you must press and hold.
A small green LED indicator light.
A Type-C power input that can run off a standard 5V power bank or phone charger.

The OSS W01 Inductance Detector is a compact, black circuit board with a pointed detection terminal at one end. It features a Type-C power input port, a detection button, and a small LED indicator light. The board is labeled with ‘W01′, ‘OSS TEAM’, and ‘INDUCTANCE DETECTOR’. Dimensions: 75mm x 27mm (approximately 2.95in x 1.06in)

I came across an advertisement for such a tester online. It claims to identify faulty components on circuit boards. I guess it’s all a hoax, though? If the green LED doesn’t light up, the component is faulty. So how can it tell? The advertisement showed testing resistors and capacitors.

OSS w01 Inductance Tester What would a product with a daily sales volume of 10,000 units look like?
https://www.youtube.com/watch?v=Mi4oGukxFTo

How It’s Supposed to Work

The marketing pitch is incredibly simple: If the green LED lights up, the inductor is functioning correctly. According to the instructions, you power up the motherboard you are troubleshooting. You plug in the W01 tester, hold down its button, and bring the pointed tip close to the inductor coil (about 1 to 3 mm away).

Green light stays on or flashes: The inductor is actively processing power; the internal coil is intact.
No light: The inductor coil is broken (open circuit) or not receiving power.

OSS TEAM W01 Type-C Inductance Tester is advertised as a Professional Repair Diagnostic Tool. The marketing promise is: If the LED lights up, the inductor is functioning correctly.

Advertisements are full of promises like:
Why This Pen-Sized Diagnostic Tool Is Revolutionizing Motherboard Repair (Hint: It Gives You ‘X-Ray Vision’)
Stop guessing component failures! Handheld tester gives clear pass/fail signal. Quality components, reinforced housing.
OSS TEAM W01 Inductance Tester, a compact and user-friendly device for rapid troubleshooting and fault detection of mobile phone inductors.
EMF Detector Type-C Inductance Tester High Precision Electronic Circuit Board Inductor Detector for Electronics Repair
Features Type-C power, rapid troubleshooting, and easy operation for mobile phone motherboard
If you’re nodding your head, you’re about to discover why thousands of repair techs are calling this pocket-sized tool their “secret weapon” against the most frustrating part of electronics repair…

I have seen an AI videos advertising these, claiming they will make your multimeter obsolete. W01 does not make your multimeter or oscilloscope obsolete. Not everyone will have a use for one of these, but if you do troubleshooting on systems with buck/boost converters for current and voltage regulation, then this could be a useful tool for doing a quick check on whether an inductor is being pulsed.

The Catch: It Doesn’t Have “Magic Vision”

The fact is that the W01 can sometimes successfully detect powered coils (if they have enough power going through them and they are not too well shielded). Sometimes the detection does not work.

While the device is a functional tool, online ads often stretch the truth. Watching how they use it…just touching around at random spots on an active circuit and they say “when the light does not come on, it is a bad component”. Some commercials show technicians using it to test resistors and capacitors and diodes. Spoiler alert: It doesn’t work on them.

The device is purely an induction and EMF tester. It detects the pulsing magnetic fields generated by a working coil. If you place it near a resistor or capacitor, the light won’t turn on—not because the component is broken, but because those components don’t generate the magnetic fields this pen is looking for.

Furthermore, metal heat sinks or shielding shells can trigger false positives by spreading interference, meaning the light might turn on even if you aren’t directly over a healthy inductor.

It can be a helpful troubleshooting tool for quick reference, but it cannot mystically diagnose your entire board. They only work for inductors that are powered with high frequency pulses. For inductors you don’t need them to be out of circuit to detect the em field generated by inductors when functioning properly. If you have a working board for comparison, you can test where you see light coming on in the working board, and then see if LED lights on the not working board.

Videos:
https://youtube.com/shorts/Mi4oGukxFTo?si=gSX3gqphKXq5ZW6L
https://youtube.com/shorts/8g822XrTB9s?si=nTPWQJiYnKNCSWkW
https://www.youtube.com/shorts/faQ0mO1lOrI

Instruction pictures
https://www.aliexpress.com/item/1005010320063815.html

Manual
https://manuals.plus/m/e92f476fbf03e51ea91d75fb8bb1c70f2db89e166420bedeb4f59ea78b0eb7e8

WARNING: The Hidden Danger of An Unenclosed Board

One of the most alarming aspects of the OSS W01 is its design. It is completely unenclosed—just a bare, exposed circuit board.Instruction manuals explicitly warn: “Place the front end close to the inductor, do not touch it, as some inductors are not insulated.”

Worse yet, some promotional videos on social media show users probing live, mains-powered electronic devices with this bare board. If an inexperienced hobbyist handles this unenclosed block, their fingers can easily slip and touch high-voltage components on the live board. This is incredibly dangerous and carries a genuine risk of electrical shock.

Video where probing live main powered device (potentially very dangerous) can be seen at
https://www.facebook.com/61577839981774/videos/-oss-inductance-detector-high-precision-electromagnetic-induction-measurement-al/868769249585152/

If you use this tool, it should strictly be confined to low-voltage motherboards (like smartphones), and you should handle it with extreme care. To avoid causing any short circuits, I recommend to add insulation around the tip of the W01 sensor (for example insulating tape or heat shrinking insulation).

Circuit analysis

Circuit diagram for the sensor part. Traced from circuit board and component values measured in-circuit

Clever inductive test probe

The circuitry is strange. Like a prototype or one that has been badly copied. It has some oddities, and the button on this unit looks like a legacy feature from the original lithium cell powered version.

This is Big Clive’s video about it. Screenshot is of his traced schematic.
https://youtu.be/VsEJgODLN6Q?si=Qfxyk_JYzV4CZZpf

Price Watch: From €1 to $17?

Perhaps the strangest thing about the OSS W01 (and its sibling, like the MECHANIC DT-001) is the wild pricing discrepancy online:
The Ultra-Cheap Tier: On websites like AliExpress, you can find this exact board selling for anywhere between €0.87 and €2.85.
The Premium Repair Tier: On specialized electronics repair sites or localized storefronts, the exact same tool is repackaged or marked up to anywhere between €16.00 and $16.99.
At less than a Euro, it’s a fun, low-risk novelty gadget to throw into your repair toolkit. At $17, the price tag starts to outpace the actual utility of a bare EMF-detecting PCB.

The Verdict: Hoax or Handy?

The OSS TEAM W01 Inductance Tester is not a hoax, but the marketing definitely pushes it into “too good to be true” territory. It won’t give you “X-Ray vision,” and it won’t replace a proper multimeter or oscilloscope. However, for a mobile phone technician who needs a 2-second check to see if an inductor coil is actively passing a signal without desoldering it, it’s a functional, handy little device. Just keep your fingers away from the live components, don’t try to use it on capacitors, and definitely don’t overpay for it!

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Parkside Cordless Screwdriver 4V PASD 4 B2 Unboxing – Test – Disassembly – LIDL Tools

Parkside VDE Electricians 4V Cordless Screwdriver Review – PASD 4 C3

Those tools come with a selection of bits, but unfortunately there is no No PZ/S bits specifically designed for electrical work.

The other downside of those is that unfortunately they use custom bits that are impossible to find replacements for. You cannot use standard bit or different bits violate 1000V insulation safety ratings. There are also other tools with insulated bits, but unfortunately the bits on this screwdriver are not compatible with other insulated bits on the market.

The different shank size is there intentionally there to avoid to put in regular 1/4″ bits (which could be dangerous when working with live circuits. If you want to use standard bits (when working with non-electrical works), the later video comments offers a solution idea: “Hello, Found a solution! If you insert a TORX 45 long bit 75 mm in there it will work. In the other end ( hex ) you can hammer in a bit adapter insert. Problem solved.” That is if you want to just skip the electrical insulation and safety parts.

Those tools have also quite low torque. They are not suitable to be used as generic screwdrivers. So those electric screwdrivers are not for finishing the job, they are for speeding the process before torking the connections to the specified torque level. It seems they copied the exact specks of the Wiha Speed E which has 0.4 Nm in electric mode and max 8 Nm in manual mode.

Expert Explains Why, Essentially, You’re Fucked | Onion Now: Focus
https://youtu.be/Bex5LyzbbBE?si=1L-ZwHRCVG9lWhPT

The research is astounding. There definitely needs to be more discourse on this topic.

Many other travel adapters only work well with ungrounded loads (typically either accept only ungrounded plug or leave ground not connected). This is one rare product that seems to handle grounding properly.

It supports many outlet types to schuko conversion. Just turn to right position – output makes contact with one plug on one side of adapter.

Pros: Universal adapter for many uses. One of the rare with proper grounding. It feels to be solid and well built. When turning the selector, power is cut before ground and connected before power. This worked well as promised.

Cons: I did not see fuse in uk adapter (would be a good idea to have 13A fuse in UK, fuse  not needed in other countries). The power source selection can turn quite easily – can turn accidentally and cut your power  output if you are moving cables. Two times more expensive than the ungrounded model.

What is inside this device and how it works. Here are some pictures to describe that.

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RFID keys are commonly used in homes, offices, hotels, and security systems, where they can be easily programmed, deactivated, or replaced. Their flexibility and reliability make RFID technology a popular choice for enhancing security and simplifying access management. An RFID system has three main parts: the key (or tag), the reader, and the control system.

RFID keys work by using radio waves to communicate with a reader, allowing quick and contactless identification. When you bring the RFID key close to a reader, the reader emits a low-power radio signal. In most access systems, the key is passive, meaning it doesn’t have its own battery, and it gets powered by the reader’s signal through electromagnetic induction. Once powered, the chip sends back its stored ID via radio waves. Inside the key—whether it’s a card or fob—there’s a tiny microchip attached to an antenna. This chip stores a unique identification code.

This image shows the “StarKey” in its assembled state.
Design: It’s designed to be rugged and waterproof. The star/flower shape in the center is the signature Verisure aesthetic.
Functionality: Each tag is uniquely registered to a specific person in the household. When you tap it against the keypad, the system logs exactly who entered or left the building.

Pro-tip: If you ever lose one of these, you should immediately log into your Verisure app and deactivate that specific tag to ensure your home remains secure!

The following images provides a rare look at the internal and external design of a Verisure StarKey (specifically the RA14 model). This is a passive RFID (Radio Frequency Identification) tag used to arm or disarm Verisure alarm systems without needing a PIN code.

Here is a breakdown of what you are looking at: Internal Components
The green circular disc is the PCB (Printed Circuit Board) that lives inside the plastic casing.
The Coil (Antenna): Notice the fine copper-colored rings around the outer edge, that is the antenna for RFID signals. Since the tag has no battery, it relies on induction. When you hold it near the Verisure VoicePad or Keypad, the reader emits an electromagnetic field that “powers up” this coil.
The “Blob” (Microchip): The black circular dome on the right is a “chip-on-board.” It contains the unique ID and encryption logic. It’s covered in epoxy to protect the delicate silicon wafer.
RA14 Marking: This is the specific model or revision number for this generation of Verisure StarKeys.
The Center Square: This area contains physical alignment guide for manufacturing and/or installinf to the casing.

Technical Details
Frequency: These typically operate on the 13.56 MHz (NFC/High Frequency) or 125 kHz (Low Frequency) band. Given the density of the coil windings visible in your photo, it looks like a high-frequency tag designed for short-range security.
Security: Unlike basic office key fobs, these use encrypted communication to prevent “cloning” (where someone could scan your pocket and copy the signal).
Convenience: The main selling point for Verisure is the “SOS” integration; if an unauthorized person forces you to disarm the system, using a specific “duress” tag (or code) can silently alert the monitoring center.

I did some testing with NanoVNA connected to magbetic field EMC measurement probe to verify the operating frequency. My measurement shows around 14 MHz resonance frequency on NanoVNA screen. This matches pretty well to 13.5 MHz frequency tag, because taking the board out from original case and the measurement arrangement can affect it’s resonance frequency somewhat.

Hacker and security researcher Samy Kamkar takes a look at a variety of hacking scenes from popular media and examines their authenticity.

Video: https://www.youtube.com/watch?v=SZQz9tkEHIg

Start with circuit from https://www.facebook.com/share/p/1GJ5iBFZDq/

Most of the power in this circuit is lost on that resistor, approximately 500 mW. That resistor needs to be able to handle that power. Anything less 0.5W power rating will burn out (fire danger) and 0.5W resistor will run very hot (potentially can damage the plastic case, fire danger if case is not made of heat resisrant msterial). A “0.5 W resistor” is typically rated to dissipate 0.5 W at 70 °C ambient, in free air, with an allowed body temperature often up to 155–200 °C (depending on type).
The resistor needs to be with at least 1W power rating, and it would still run pretty hot (80–125 °C).

Second circuit from https://www.facebook.com/share/p/1CK3psPmdA/

How does the circuit work with 220V?

The 220V LED bulb driver circuit works by using a capacitor (47uF 25V) to drop the voltage and limit the current to the LED. Here’s a simplified explanation:

1. The 220V AC power is applied to the circuit.
2. The capacitor (47uF 25V) acts as a reactance, reducing the voltage and limiting the current.
3. The diode (1N4007) rectifies the AC voltage, converting it to a pulsating DC voltage.
4. The resistor (56k) helps to further limit the current to the LED.
5. The LED bulb is connected across the circuit and lights up when the current flows through it.

This circuit is a simple and cost-effective way to drive an LED from a high-voltage AC source. However, it might not be suitable for long-term use due to potential voltage spikes and capacitor reliability issues.

Keep in mind that working with 220V AC can be hazardous, and proper safety precautions should be taken when building and testing such circuits. This is not a project for a beginner.

If you are used to calculating LED current of 20 mA with 3V voltage drop over the, you might wonder the component values. If you try to calculated the LED resistor for 20 mA, you would get 10850 ohms, not 56k like used in this circuit.

This circuit does not run the LED at 20 mA, but lower 4 mA current limited by resistor (only half of time). That lights up LED, but not at full brightness. With this circuit the resistor wastes 500mW power. If you change the resistor to your 10850 ohms, the power loss in resistor would be almost 5 watts (you would need a quite big power resistor that would not fit inside the case).

Why there is the series diode in the circuit? Isn’t an LED by definition a diode?
Yes. LED is diode, but they typically quite limited how much reverse voltage they can withstand (many LEDs have a 5V limit for safe reverse voltage). Another reason that there is also a capacitor to avoid the LED flickering at mains 50 Hz frequency. A diode is needed for charging the capacitor to DC that can power LED on the negative half wave the diode blocks.

And what would be the purpose of the capacitor?
With one diode rectifier, LED would flicker half time on and half time off at 50 Hz rate. That kind of LED looks flickering. Add a capacitor, and LED will stay on all the time without noticeable flickering.

I understand the current limiting of the Resistor but shouldn’t that be on the hot leg versus the neutral leg?
This kind of plug can be plugged in both ways so in circuit you can’t control if resistor get plugged to phase or neutral. There is no practical difference as long as the circuit is inside well insulated case.

Final comment: Learn from those circuits, but I don’t recommend building them. The circuits are potentially dangerous (electrocution and fire dangers). They also have very low efficiency (most power input is wasted as heat on the resistors).

This basic circuit published at https://www.facebook.com/share/p/1Gi4UZHpVh/ claims to be able to serve as an instantaneous way for you to detect whether it is in fact due to a blown fuse or not. It is a small circuit that tries to make your job as an electronic technician easier.

When the fuse is in working order the LED remains “off.” When the fuse has blown, however the LED lights up to provide you with an obvious notification of the blown fuse condition. Therefore, you do not need to guess or waste time continually re-checking the same device as this simple idea can save so much troubleshooting time and effort when working with power supplies or batteries.

#innovation #learning #electronicproject #simplecircuit

Could this build in a simpler way?
Why not simplify the circuit by wiring the LED directly across the fuse ( with a current limiting resistor )

Source: https://theorycircuit.com/electronics-projects/blown-fuse-indicator/

The downside of his idea:
1. When fuse blows, there is no reliable full isolation of load because of the current through LED
2. If load is removed, LED does not indicate blown fuse

Another way it so place a power indicator across the supply after the fuse. It works by showing if power gets through the fuse or not. The downside is that the indicator LED will consume power all the time when power is on.

Links to other ideas:
https://dmohankumar.wordpress.com/2015/10/21/blown-fuse-indicators-simple-design-10/
https://www.eevblog.com/forum/projects/blown-fuse-indicator-design-validation-automotive/
https://electronicsarea.com/blown-fuse-indicator-circuit-using-one-transistor/
https://theorycircuit.com/electronics-projects/blown-fuse-indicator/
https://www.edn.com/simple-blown-fuse-indicator-sounds-an-alarm/