Non-Linear Junction Detectors
How to choose a non-linear junction detector
Why these exist
Every other detection method depends on the device doing something. A signal detector needs it to transmit. A lens detector needs line of sight to the optics. A device switched off inside a wall cavity, a piece of furniture or a power outlet defeats both. A non-linear junction detector transmits a signal and listens for the harmonics that semiconductor junctions produce when energised. Almost any circuit board responds, whether powered or not.
Who uses them
Corporate security teams before board meetings, legal and financial firms handling sensitive matters, and professionals conducting sweeps for clients. Carrying one is what separates a professional search from a consumer check, because it finds a device whether or not it is powered, and interpreting the response is what the training and the price are for. If you are checking your own home or car occasionally, a combined signal detector and lens detector is the appropriate tool.
Compare the types
 Cayman ST-402 |  Lornet Star 24 |  Lornet 36 | |
|---|---|---|---|
| Transmits | 2 to 3GHz | 800, 2400 or 3600MHz on interchangeable modules | 3.6GHz through a 16 degree parabolic antenna |
| Reach | Telescopic bar to 1.5 metres, for ceilings and cavities | Depends on the module fitted | A narrow beam for large rooms and long reach |
| Reads | Harmonics on three LED bars, with audio | Second and third harmonics | Second and third harmonics, compared to tell a circuit from corroded metal |
| Suits | A sweep team that needs to reach high and deep | Different building fabrics on the same job | Enterprise sweeps |
| See | Cayman ST-402 | Lornet Star 24 | Lornet 36 |
Buying guides
Counter-Surveillance Buying Guide NZHow to find hidden cameras, bugs and trackers
Non-linear junction detectorsJump to this section of the Counter-Surveillance Buying Guide
Related
Counter Surveillance Listening Device Detectors Hidden Camera Detectors
Common questions
Does it need the device to be on?
No. That is the entire point: it finds electronics regardless of power state.
Will it react to ordinary electronics?
Yes, and to some corroded metal joints. Comparing the second and third harmonics is how the better units tell a semiconductor from a rusty nail, and interpreting the response is what the training is for.
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).