Counter Surveillance
How to choose counter-surveillance equipment
Three ways to find a device
Most hidden devices transmit, and a signal detector finds anything broadcasting on 4G, WiFi, Bluetooth or radio, covering the majority of cameras, trackers and bugs in one sweep. But a camera recording to a memory card does not transmit, so a signal detector will not find it. That is what a lens detector is for: it flashes light and finds the reflection from a lens, transmitting or not. Devices that are switched off entirely defeat both methods, which is what non-linear junction detectors are for.
Start with what you are actually looking for
The four things people search for are cameras, microphones, trackers and phone tampering, and no single device covers all four well. If it is a room you sleep or change in, a camera is the concern and an optical lens finder is the tool. If it is a conversation, a microphone is the concern and a radio detector is the tool. If it is your movements, a tracker is the concern and the search is physical as much as electronic. A microphone blocker takes the other approach and makes recording useless rather than finding the recorder.
Compare the types
 Lens finder |  RF detector |  Combined |  Non-linear junction detector |  Voice recorder blocker | |
|---|---|---|---|---|---|
| Finds | Any camera lens, transmitting or not | Anything transmitting: cameras, bugs, trackers | Lenses, transmissions and magnet mounted trackers | Electronics, powered or not | Nothing: it makes recording useless instead |
| Misses | Microphones and trackers | Anything recording to a card or switched off | Devices switched off in a cavity | Needs training to read | Cameras |
| Takes | A slow sweep by eye, lights off | Minutes, after clearing your own signals | Both passes | A professional sweep | Switch it on |
| Suits | Hotel rooms, rentals, changing rooms | Offices, meetings, a first check of a room | Most people checking their own space | Corporate and legal sweeps | Boardrooms, meetings, vehicles |
| Range | Hidden camera detectors | Listening device detectors | GPS tracker detectors | Non-linear junction detectors | Microphone blockers |
Buying guides
Counter-Surveillance Buying Guide NZHow to find hidden cameras, bugs and trackers
The four detection methodsJump to this section of the Counter-Surveillance Buying Guide
How to actually sweep a roomJump to this section of the Counter-Surveillance Buying Guide
Related
Hidden Camera Detectors Listening Device Detectors GPS Tracker Detectors Non-Linear Junction Detectors Microphone Blockers Geiger Counters
Common questions
Which should I start with?
A combined signal and lens detector covers the most ground for the money. Sweep more than once and at different times, because a tracker reports on a schedule and a transmitter sends in bursts.
Can I check a car for a tracker myself?
Yes. GPS tracker detectors with a magnetic probe are made for searching wheel arches and the underbody, and a physical search of the likely spots finds what a radio pass cannot.
Why did it go off in an empty room?
Because it found your phone, your laptop, your smart speaker or a neighbour's router. Put your own devices in flight mode or out of the room, then set the sensitivity so the unit responds to a known source and nothing else. Without that baseline you are reading noise.
When is equipment the wrong answer?
When you have a specific, credible reason to believe you are being monitored. A handheld unit suits a precaution, a hotel room, a rental or a periodic office check. A methodical search of a whole property or vehicle needs equipment that also finds devices which are switched off, and a situation that serious may warrant going to the Police as well.
Is it legal to sweep for hidden cameras and bugs in New Zealand? NZ law
Yes. Owning and using a detector needs no licence, and sweeping a room, a car or an office you control, or one you have the occupier's permission to check, is lawful. If you find something, leave it where it is, photograph it and go to the Police, because the device is evidence. A hidden camera in a bathroom or bedroom, a listening device on a conversation the person who placed it is not part of, and a tracker put on your car by someone else can be offences under the Crimes Act 1961 (sections 216G to 216J, section 216B, and since 26 May 2026 the stalking sections 216O to 216Q).