Listening Device Detectors
How to choose a listening device detector
What a signal detector finds
Nearly every modern surveillance device transmits: a WiFi camera streaming footage, a 4G bug carrying audio, a GPS tracker reporting location. A signal detector sweeps the radio spectrum and alerts on any of them, which is why one device covers what would otherwise need three. What it cannot find is anything not transmitting: a camera recording to a memory card, or a device switched off. For those, see lens detectors and non-linear junction detectors.
Clear the room of your own signals first
Start by turning off everything of your own that transmits: phones on flight mode, laptops off WiFi, smart speakers unplugged, because a detector has no way to tell yours from anyone else's. Then work the room slowly at low sensitivity, raising it until the unit responds to a known source, and sweep close to surfaces rather than waving it around, because signal strength falls away quickly with distance. Entry level units tell you a signal is present and roughly where; professional units identify the frequency and type, which is what tells a hidden device from a neighbour's router.
Compare the types
 Pen detector |  Handheld RF detector |  Professional RF detector | |
|---|---|---|---|
| Tells you | A signal is present and roughly where | Where it is, with a directional antenna to walk in on it | What it is, across 26 bands |
| Also finds | Nothing else | Magnet mounted trackers, powered or not | GPS trackers in a dedicated mode |
| Runs on | One AA cell, 10 to 20 hours | Check the listing | Check the listing |
| Suits | A hotel corridor or a shared office, quietly | A room you check now and then | Regular sweeps in a busy building |
| See | Protect 1205M pen detector | RF bug detector with dual antenna | iProtect 1217 |
Buying guides
Counter-Surveillance Buying Guide NZHow to find hidden cameras, bugs and trackers
The offline voice recorder problemJump to this section of the Counter-Surveillance Buying Guide
Non-linear junction detectorsJump to this section of the Counter-Surveillance Buying Guide
Related
Counter Surveillance Hidden Camera Detectors GPS Tracker Detectors Non-Linear Junction Detectors Microphone Blockers
Common questions
Will it react to my own WiFi?
Yes, and that is expected. The skill is in narrowing down by moving through the room and watching signal strength.
What does a bug look like in practice?
Almost never a device that looks like surveillance equipment. It is a mains adaptor, a USB charger, a power board, a desk clock, a pen left behind, or a small sealed box taped inside a cavity. The giveaway is rarely the object and usually the circumstance: something in the room that nobody can account for.
Can it check a car?
Yes. For underbody searching specifically, see GPS tracker detectors with a magnetic probe.
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).