Counter-Surveillance Buying Guide NZ: How to Find Hidden Cameras, Bugs and Trackers

There are four ways to find a hidden device, and each one is blind to what the others catch. Radio scanning finds things that transmit. Optical scanning finds lenses whether or not they are powered. Magnetic scanning finds trackers stuck to metal while they sleep. Non-linear junction detection finds any semiconductor at all, powered or not, and it is the only method that finds an offline voice recorder. A detector that does one of these misses the rest completely, and that single fact decides almost every purchase on this page.

This guide covers thirty-four devices from the Counter-Surveillance range, $166 to $21,800. It explains what each detection method physically can and cannot see, how to actually sweep a room rather than wave a detector around in it, and where New Zealand law sits on both finding devices and blocking them.

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The Four Detection Methods

Read this section before you look at a single price. It is the whole guide compressed into three paragraphs, and it explains why the cheapest detector here is sometimes the correct buy and the most expensive one is sometimes useless.

1. Radio frequency, which finds things that are transmitting

An RF detector listens for radio energy and tells you it is getting stronger as you walk towards the source. It finds live WiFi cameras, 4G and 5G bugs, Bluetooth devices, GSM listening devices and active GPS trackers.

What it cannot see: a camera recording to an SD card with no network connection, a wired camera on a closed circuit, a voice recorder in a bag, a GPS tracker asleep between pings, and anything switched off. A large share of the devices in our own Hidden Cameras range record to a card with no radio at all, and an RF sweep will walk straight past every one of them.

2. Optical, which finds lenses whether they are on or off

An optical detector fires infrared light through a filtered red viewfinder. A camera lens is a retroreflector, so it bounces that light straight back at you as a bright point that does not move as you shift your head. It works on wired cameras, dead cameras, cameras with the batteries out, and cameras that have never touched a network.

What it cannot see: anything without a lens. Voice recorders, listening devices and GPS trackers are all invisible to it. It also needs you to be looking from roughly the same angle the camera is looking, which is why sweeping is slow and methodical rather than quick.

3. Magnetic, which finds trackers that are asleep

A magnetic probe detects the neodymium magnets that hold a GPS tracker onto a vehicle. This matters because most trackers sleep between position reports to save battery, and a sleeping tracker transmits nothing at all. An RF sweep of a car can come back completely clean while a tracker sits in the wheel arch waiting for its next ping.

What it cannot see: anything not attached magnetically, including hardwired trackers spliced into the vehicle loom, and everything indoors.

4. Non-linear junction, which finds electronics that do nothing at all

A non-linear junction detector transmits RF energy and listens for the harmonics that come back. Semiconductors, meaning the transistors and diodes inside any electronic device, return a distinctive second and third harmonic that natural materials do not. Because a transistor has that property whether or not current is flowing through it, an NLJD sees electronics that are switched off, out of battery, or have never been turned on.

This is the only method that answers the hardest question in the category, and the one the other three cannot touch: is there an offline voice recorder in this room. See The Offline Voice Recorder Problem immediately below.

What it cannot see: nothing electronic, which is the point. Its limitations are cost and skill instead. It responds to every semiconductor in range, including the wiring in the wall, a calculator in a drawer and corroded metal joints that mimic a junction, so reading one is an acquired skill rather than a matter of watching a bar rise.

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Quick Picks

Seven situations that cover most buyers. Everything else is in the comparison table below.

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Detectors Compared

Sorted by price. The Finds column is the one that matters: RF means transmitting devices, Lens means cameras on or off, Magnet means sleeping GPS trackers.

Swipe the table sideways to see every column.

Prices are NZD and were correct at the review date at the foot of this guide. The five non-linear junction detectors have their own section below.

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The Offline Voice Recorder Problem

This is the blind spot in the whole category, and almost nobody selling detectors will tell you about it, so here it is plainly.

Take a $88 USB stick voice recorder. It has no radio of any kind, so an RF detector at any price reads nothing. It has no lens, so an optical sweep passes over it. It has no magnet, so a magnetic probe ignores it. It has no indicator lights and makes no sound. It records for 28 hours on one charge and stores everything locally on its own memory. We sell one, and so does every other retailer, and you can buy the same thing at a service station.

No detector under $15,000 will find it. Not the $443 all-rounder, not the $1,206 Protect 1207i, not the $5,444 iProtect 1217. Those are all radio instruments, and a device that emits no radio is not a difficult target for them, it is an invisible one.

The same is true of a dictaphone in a jacket pocket, a card-recording camera with the WiFi disabled, and a listening device planted and left switched off until the day it matters. Our own Voice Recorders guide covers models running 300 hours continuously with no lights and no network at all. If you want to understand what you are up against, read it, because that is the actual threat in a boardroom rather than the transmitting bug people imagine.

One partial answer sits below all of these. VIM-CAMFINDER3 at $211 carries a dedicated voice recorder sensor alongside its RF and lens modes, which picks up the electronic signature that an active recorder gives off. That is a real capability and nothing else at this price has it. Be clear on the limit: it detects recorders that are running and emitting something, and its own documentation notes that a device with no electronic emission may not be detected. It does not find a recorder that is switched off. Treat it as a useful extra layer, not as a substitute for the three answers above.

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Non-Linear Junction Detectors

Five instruments, $15,468 to $21,800. This is professional TSCM equipment, not consumer gear, and the price reflects what it does rather than how it is built.

All five work the same way: transmit RF, read the second and third harmonic response from semiconductor junctions, and distinguish a real electronic device from natural materials and from corroded metal that mimics a junction. All five find devices that are powered off. What separates them is range, antenna type and how much the instrument helps you interpret what it found.

• Cayman ST-401 (403), $15,468. The entry instrument. 2 to 3GHz, under 2W peak, elliptic antenna, stepped manual sensitivity for close-in work, LED bars plus audio monitoring, standard rechargeable cells and a shock-proof transport case. Built for parcel and mail screening, furnishings, and personal effects.
• Cayman ST-402, $15,468. Same detection performance, different ergonomics. A telescopic bar with an armrest, which is what you want when a sweep runs for hours and you are reaching into ceilings and wall cavities. Also specified as interference resistant for difficult RF environments.
• Lornet Star 24, $17,794. A step up in capability. Modular antennas at 800MHz, 2400MHz and 3600MHz so you can match the band to the environment, dual-harmonic verification on both second and third harmonics, selectable pulse and continuous-wave modes, automatic channel tuning with anti-jamming filtering, and up to 50 metres in pulse mode with sub-metre pinpointing in CW. The 50 metre figure is the reason to move up from the Caymans: it turns a room-by-room search into a wide scan followed by targeted confirmation.
• Lornet Star 24S, $21,800. The Star 24 plus an integrated spectrum display and headphone monitoring, a removable telescopic rod extending 54 to 86cm, hot-swappable antenna modules, and manual power and receive sensitivity controls on the handle itself. The display is the real upgrade, because it lets you show a client what you found rather than describe it.
• Lornet 36, $21,800. A different tool for a different job. A 3.6GHz parabolic antenna, 3581.5 to 3607.5MHz, pulse peak 18W, producing a narrow beam for finding electronics at stand-off distance. Use it where you cannot get close to the surface you need to check: high ceilings, behind glass, across a large room, or anywhere approaching the target would announce the search.

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Voice Recorder Blockers

These do not find anything. They make recording useless, which is a different and sometimes better answer. Ultrasonic emitters push sound above the range of human hearing into the room; microphones fold that energy down into their own audio path and record noise where speech should be. You hear the conversation normally. A recorder does not.

Two things decide which one you buy: how big the protected area needs to be, and what the device has to look like while it does it.

• Rabbler MNG-300, $651. Works differently from the rest. Instead of ultrasonics it fills the room with dynamic, voice-like sound, so a recording captures speech-shaped chatter that cannot be separated from the real conversation. About 3 metres. Boardroom and meeting room use.
• VIM-GSM-3, $768. A wireless charger with two compartments. Phones go in, charge, and have their microphones neutralised while they sit there. For the specific problem of phones on a meeting table.
• VIM-BLOCK4, $868. Disguised as a working 6000mAh power bank with real USB-A, USB-C and Micro-USB ports and an LED display. Remote controlled, about 1.5 metres. The one for when the blocker itself should not be visible.
• VIM-BLOCK6, $980. Sixteen sensors firing in a 360 degree pattern, sized for a car cabin and shaped to sit in a cup holder.
• VIM-BLOCKONE, $1,102. Air purifier disguise, 28 emitters, about 6 metres, 0.53kg, 3 hour battery, remote activation. The travelling option.
• VIM-BLOCKPRO, $1,213. A Bluetooth speaker that plays music and protects about 6 metres across a 270 degree arc, roughly a 16 square metre room.
• VIM-BLOCK3, $1,557. 360 degrees to 6 metres with directional control so you can concentrate output where the risk is. Battery for quick deployment or mains for long sessions.
• VIM-BLOCKTWO, $1,614. Voice activated, so it engages the moment speech starts and idles the rest of the time. Remote operation means you never have to walk over to it.
• VIM-BLOCK5, $1,837. Seventy-two ultrasonic speakers in one array, 360 degrees. The most output here.

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Mistakes That Cause Returns

Almost every disappointed counter-surveillance customer made one of these seven mistakes, and none of them are the detector's fault.

1. Buying any RF detector to find an offline voice recorder. A recorder with no radio, no lens and no lights cannot be found by radio, optical or magnetic detection at any price. Only a non-linear junction detector will locate it, or a blocker will make it pointless. This is the most expensive mistake in the category because people buy up the RF range looking for a device the whole method is blind to. See The Offline Voice Recorder Problem.
2. Expecting an RF detector to find a camera that is switched off. This is the big one. A card-recording camera with no network connection emits nothing. You can stand next to it with a $5,444 instrument and get a flat reading. If your worry is a concealed camera, you need optical detection, not radio.
3. Sweeping with the WiFi still on. A modern house is saturated: router, mesh nodes, phones, watches, TV, speakers, doorbell, printer. Every one of them lights up an RF detector. Turn off the WiFi at the router and put every known device in flight mode before you start, or you will spend an hour chasing your own hardware.
4. Buying a detector that stops below 3.5GHz. Spark, One NZ and 2degrees all run 5G on the 3.5GHz band. A detector with a ceiling of 2.5GHz cannot see a 5G device at all. Check the upper frequency limit before you check anything else.
5. Sweeping a bathroom with a cheap lens finder. Tiles, mirrors, taps and shower screens throw back reflections constantly, and after the twentieth false hit people stop believing the device. Either use something with IR-filtering glass like the WEGA-i, or accept that this room takes ten times longer than the others.
6. Doing the optical sweep with the lights on and stopping there. A 940nm night vision camera is invisible in daylight and glaringly obvious in a dark room through the right mode. Sweep twice, once lit and once dark.
7. Checking a car for trackers with a signal detector only. Most trackers sleep between reports. A clean RF sweep of a vehicle proves very little on its own. You need the magnetic probe, and you need to run it slowly along the metal.
8. Buying a blocker when the problem is a camera. Ultrasonic blockers defeat microphones. They do nothing whatsoever to a camera, a tracker, or anything that has already been recorded. Detection and denial solve different problems.

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How to Actually Sweep a Room

A detector in the hand is about a third of the job. This is the sequence that finds things, and it is deliberately slow.

Before you turn anything on

Kill the noise first. Switch off the WiFi at the router, not just on your phone. Put every phone, tablet, watch and laptop in the room into flight mode. Unplug smart speakers, the TV and anything with a standby light. What is left transmitting is what you are looking for.

Then look with your eyes before you look with the instrument. Anything with a lens has to have a clear line of sight, so it cannot be behind fabric or inside a drawer. Stand where a camera would need to stand: facing the bed, the desk, the shower, the till. That narrows a whole room to a handful of objects.

The RF pass

Start at the lowest sensitivity that still reads something and walk the perimeter slowly, holding the detector out from your body. When the reading rises, do not chase it directly. Reduce sensitivity and walk the same area again, and repeat. Each reduction shrinks the radius the detector responds to, so the source is progressively cornered. Chasing at full sensitivity just tells you the signal is somewhere in the room, which you already knew.

Pay attention to objects that have a reason to be powered: alarm clocks, chargers, smoke detectors, power boards, routers, speakers, photo frames. Our own Hidden Cameras guide is a useful list of exactly what to be suspicious of, because it is the same catalogue of objects.

The optical pass, lights on

Hold the viewfinder against your eye and sweep slowly across every surface, moving your head rather than just your hand. A lens returns a bright point that stays fixed as you shift position, while ordinary reflections slide and change. Cover the room from several standing positions and at least one sitting or lying position, because a camera aimed at a bed is best seen from the bed.

The optical pass, lights off

Same sweep in the dark, in infrared mode if the device has one. This is the pass that catches night vision cameras and the one people skip. Give your eyes a minute to adjust first.

The physical pass

Instruments do not open things. Check inside smoke detector housings, behind wall clocks, under the lip of desks and shelves, inside power boards, behind headboards, in air vents and under bedside tables. Look for cables that go somewhere they should not, screws that are newer than the fitting around them, and dust patterns that show something has been moved recently.

What none of these passes will find

Everything above finds transmitting devices, lenses and magnets. A voice recorder sitting switched off in a drawer, or running silently in a bag, survives every one of these passes intact. If ruling that out is the point of the sweep, you need a non-linear junction detector or a booked sweep, and no amount of care with a consumer instrument substitutes for it. Say so to anyone who asks you to sweep their boardroom.

The vehicle pass

Run the magnetic probe slowly over wheel arches, the underside of bumpers, the tow bar area, the boot floor and the underside of seats. Then check the OBD port under the dash, which needs no magnet at all because trackers plug straight into it. A hardwired tracker spliced into the loom will not respond to a magnet and will usually need a workshop to find.

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Key Specs Explained

Frequency range, and why the top number matters most

An RF detector covers a band, quoted as something like 10MHz to 8.6GHz. The bottom number is rarely a problem. The top number decides whether the device can see modern equipment at all. New Zealand 5G runs on 3.5GHz, WiFi runs at 2.4GHz and 5GHz, and WiFi 6E extends to 6GHz. A ceiling of 8.6GHz or 12GHz covers all of it comfortably. Anything under 3GHz does not.

Number of channels

A single-channel detector gives you one reading for all radio energy combined. A multi-channel instrument like the Protect 1207i splits it into six, so WiFi activity does not mask a GSM bug sitting underneath it. In a building full of normal radio traffic, channels are what turn a detector into an instrument.

Sensitivity adjustment and attenuators

Sensitivity control is how you locate rather than merely detect. Turning it down repeatedly as you close in is the actual technique, and a detector without adjustment can only tell you that something is somewhere. An attenuator does the same job at the top end, letting you work close to a strong source without the meter simply pinning.

Optical detection distance

Quoted lens detection runs from about 3 metres on compact units to about 10 metres on the WEGA-i and VIM-BUGDETECT14. Three metres is enough for a hotel room. It is not enough for a boardroom or an open-plan office, where you would otherwise have to sweep from a dozen positions.

IR filtering

The difference between a detector that flags every shiny object and one that flags lenses. Filtered glass rejects the diffuse reflection from mirrors and chrome while passing the sharp retroreflection from a lens. It is the main reason optical detectors vary in price by a factor of four.

Magnetic probe reach

Short by nature, around 20cm on the units that quote it. That is not a weakness; it is how you localise. You are looking for the point where it triggers, not for a long-range alert.

Runtime

Underrated. A full sweep of a house takes hours, and the useful figures here range from about 5 hours on compact units to 25 hours on the VIM-CAMFINDER. Standby matters too, because a detector bought for peace of mind lives in a drawer between uses and needs to work when it comes out.

Non-linear junction detection, the professional tier

An NLJD transmits RF energy and listens for the harmonics that semiconductors return. Because transistors and diodes respond whether or not they have power, it finds electronics that every other method misses: offline voice recorders, dead bugs, cameras with the battery removed, devices waiting to be switched on. Five instruments from $15,468 to $21,800 compared in Non-Linear Junction Detectors above. They are operator-skill instruments rather than consumer products, which is why a booked sweep is usually better value than owning one.

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Choose by Situation

Staying somewhere you do not own

Holiday rentals, motels, holiday parks and short-stay apartments. The threat is a camera, so buy optical. WEGA-i at $635 if you travel often and want the bathroom sweep to be quick, or VIM-CAMFINDER6 at $222 for the dark-room mode at a third of the price. Sweep the bathroom, the bedroom and anything facing the bed first.

You think there is a tracker on your vehicle

VIM-BUGDETECT15 at $445. The magnetic probe is not optional for this job. Before you touch anything you find, read If You Find Something below, because in New Zealand this is now specifically named conduct under the stalking offence and the device is evidence.

Relationship or family safety

The most common real reason people buy these, and the situation where the device matters least. A combination unit such as VIM-BUGDETECT14 at $445 covers cameras, trackers and transmitters in one sweep, which is right when you do not know what you are looking for.

Please also get human support alongside the equipment. Women's Refuge and Netsafe both deal with technology-facilitated abuse specifically and can help with the parts a detector cannot: account access, shared phone plans, cloud backups and family sharing, which is how location is leaked far more often than through any hidden device. If you are in immediate danger, call 111.

Commercial and boardroom

Where the risk is a recorded conversation rather than a planted camera, denial usually beats detection because you cannot search the people in the room. Rabbler MNG-300 at $651 for a meeting table, VIM-BLOCK3 at $1,557 for a full room. If you also need to sweep, do it with a multi-channel instrument so normal office radio traffic does not swamp the reading.

Professional, repeated use

Investigators, security consultants and anyone sweeping for clients. Protect 1207i at $1,208 is the working instrument, Protect 1216i at $1,408 adds signal signatures you can show a client, and iProtect 1217 at $5,453 gives per-band analysis. Add an NLJD only when clients need dormant devices ruled out.

You would rather someone else did it

Reasonable, and often the right call. A thorough sweep uses several thousand dollars of instruments and, more importantly, an operator who has done it before and knows what a normal building looks like on a meter.

We supply the equipment rather than the service. If you want a sweep carried out for you, engage a counter-surveillance or TSCM specialist operating in New Zealand. Ask what instruments they bring, specifically whether a non-linear junction detector is included, because an RF-only sweep cannot rule out a device that is switched off.

This is often the better value if you need it once. A thorough sweep uses several thousand dollars of instruments and, more importantly, someone who has done it before and knows what a normal building looks like on a meter. Buying a $443 detector to answer one urgent question is reasonable; buying a $5,444 one is usually not.

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If You Find Something

What you do in the next ten minutes matters more than the detector did.

1. Do not remove it, and do not switch it off. The instinct is to rip it out. Resist it. Removing the device destroys where it was, how it was fixed, and often what it was recording, and those are the parts that establish who put it there.
2. Photograph it in place. Wide shot showing the room, medium shot showing the position, close shot showing the device and any serial number. Include something for scale. Note the date and time.
3. Do not talk near it. If it is a listening device it is still listening, and if it is a camera it is still watching. Move to another room before you discuss what to do.
4. Call the police. Covert recording in a private space, and tracking a person, are criminal matters in New Zealand, not just unpleasant ones. Ring 111 if you feel unsafe or 105 to report something after the fact.
5. If it is on a vehicle, leave it there until you have advice. A tracker in place tells the police something. A tracker in your kitchen drawer tells them very little, and the person who fitted it will know within hours that it stopped moving.
6. Write down the timeline. When you first suspected something, what made you suspect it, who has had access to the space or the vehicle, and when. Do it while it is fresh.
7. Check the non-physical routes as well. Far more location leaks come from shared accounts than from hardware: family sharing, find-my-device services, shared cloud backups, a phone plan in someone else's name, a car app still linked to a previous owner. A detector cannot see any of that. Netsafe can help you work through it.

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FAQs

Can any detector find a voice recorder that is not transmitting?

Only a non-linear junction detector, from $15,444. A recorder with no radio, no lens and no lights is invisible to every RF, optical and magnetic instrument regardless of price. The practical alternative is a voice recorder blocker from $650, which makes the recording useless without ever finding the device.

Why can a $5,444 detector miss a $88 voice recorder?

Because they are radio instruments and it emits no radio. Price buys sensitivity, band coverage and channel separation, all of which are useless against a device that transmits nothing. This is a limit of the method, not of the product.

Can a detector find a camera that is turned off?

An optical lens finder can, because it works on reflection from the lens rather than on any signal. An RF detector cannot, because there is nothing to detect. This single difference is the most common reason a detector disappoints someone.

Will these find a hidden camera in my accommodation?

An optical detector will find any camera with a clear line of sight, which every useful camera must have. Sweep the bathroom, anything facing the bed, and smoke detectors and clocks in particular. Do one pass with the lights on and one in the dark.

Are voice recorder blockers legal in New Zealand?

The ultrasonic blockers on this page emit sound, not radio, so they sit outside the Radiocommunications Act 1989 and are legal to own and use. Radio jammers, including mobile phone jammers, are a different thing and operating one without a licence is an offence. We do not sell them.

What frequency range do I actually need in New Zealand?

Up to at least 6GHz, and preferably more. Local 5G runs on 3.5GHz, WiFi on 2.4GHz and 5GHz, and WiFi 6E to 6GHz. Detectors here reach 8.6GHz or 12GHz, which covers everything in normal use.

Why does my detector go off constantly?

Because your house is full of radio. Turn the WiFi off at the router, put every device in flight mode, unplug smart speakers and the TV, then sweep. Also start at low sensitivity and raise it, rather than the other way around.

Can I find a GPS tracker without a magnetic probe?

Only while it is transmitting, which for most trackers is a few seconds every several minutes. A signal-only sweep of a vehicle can easily come back clean with a tracker present. Use the magnetic probe, and also check the OBD port under the dash.

Is a $443 detector good enough, or do I need the $1,206 one?

For one situation in one property, the $443 combination unit is the right buy and covers all three detection methods. The professional instruments earn their price through channel separation and repeatability, which matter when you sweep regularly and have to justify the result to someone else.

Should I just book a sweep instead?

If you need it once and the stakes are high, usually yes. A booked sweep brings instruments worth several thousand dollars and an operator who knows what a normal building reads like, which is the part no product spec gives you.

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Responsible Use in New Zealand

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Related Guides

This guide is about finding devices. These cover the devices themselves, which is the fastest way to learn what to look for.

• Hidden Cameras is effectively the target list. Clocks, smoke detectors, chargers, speakers, routers and power banks are the objects to be suspicious of, and that guide names them.
• Voice Recorders for what an audio device looks like and how small it now gets, which is why the blockers on this page exist.
• GPS Trackers for how trackers attach, how often they report and where they are usually fitted. Useful reading before you sweep a car.
• Pen Cameras for the smallest end of concealed recording, and the reason a desk sweep is worth doing.
• WiFi Security Cameras if what you actually want is to monitor your own property openly rather than find someone else's device.
• Night vision optics buying guide for thermal imaging, which finds a person or a warm device in the dark when a radio detector finds nothing.

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Shop Counter-Surveillance

The shortest path is one question: do you know what you are looking for. If you do, buy the single-method tool that finds it. If you do not, buy a combination unit that runs radio, optical and magnetic detection together, and start at $332.

The thirty-four above cover every method and price tier.

Browse all Counter-Surveillance, or narrow to Spy Camera Detectors, GPS Tracker Detectors, Microphone Blockers, Listening Device Detectors or Non-Linear Junction Detectors.

Last reviewed August 2026.