Gear: what works, what's theater

Do detector apps actually work?

The most-downloaded tools in this category are the least useful — and there's a controlled, peer-reviewed test that says so.

The study the listicles won't cite

Researchers at the University of Wisconsin–Madison and NYU (published at USENIX Security 2023) planted real hidden cameras, microphones and trackers in a controlled environment and ran eleven popular detector apps against them. The result: nine of the eleven showed no coherent reaction to a device being present at all. The two that did react were only reliably useful within about two centimeters of the device — meaning you'd already have to know where it was. A phone's magnetometer and radio simply cannot do what dedicated hardware does. Magnetic-field detector apps: same problem, weaker.

One caution from the same research tradition: beware "independent tests" published by sites that sell the winning app. Check who runs the site before you trust the score.

The honest gear ranking

✅ The flashlight / optical method — free and real. Works on cameras that transmit and cameras that don't. Controlled testing says the eyes-plus-light approach is still the most reliable method, gadget or no gadget.
✅ A dedicated optical lens-finder (~$15–30) — genuinely useful. A ring of red LEDs you look through that makes lens glints obvious. It finds the lens, not a signal, so it works on wired, wireless, and offline cameras alike.
⚠️ A dedicated RF detector (~$40–50) — real physics, real limits. It picks up wireless transmissions a phone can't, and it's the right tool for transmitting audio bugs. But be skeptical of the "85–90% effective" figures in buying guides — they trace to marketing copy, not independent testing. The same lab study found the common all-in-one design usable but placement-sensitive, noisy (your own devices, the router, the neighbors' Wi-Fi), with a magnetometer useless past about an inch and a lens-finder prone to false positives on anything reflective. Treat a beep as one signal to investigate, not a verdict.
❌ "Hidden camera detector" phone apps — theater. The one legitimate phone tool is a plain network scanner (Fing/Wifiman), and that's a network scan, not a detector.

If you do carry an RF detector

Airplane-mode everything of your own first, or you'll chase yourself around the room. Walk slowly, hold it near objects rather than waving it in the air, and turn the sensitivity down as you close in so you can localize. The skill isn't "does it beep" — it's "does it beep more the closer I get to this specific object."

Cover: The Traveler's Counter-Surveillance Field Manual

The Field Manual — PDF edition

The full gear chapter — including how audio bugs differ — is in the book. The complete system — every check on this site plus the ten-minute walkthrough, audio devices, your legal rights, and what to do if you find something. 47 printable pages, instant download, keep it on any device.

Get the Field Manual — $27

Prefer Kindle? $7.99 on Amazon.

Keep going

The 90-second room sweepFour steps, no gear — the check to run when you arrive. Find hidden cameras in an AirbnbWhere devices actually hide, and the rules hosts must follow. The flashlight trickThe one free method that catches a camera even when it is off. The two-way mirror testWhy the fingernail trick doesn't work — and what does. Find a GPS tracker on a carThe 60-second check, plus the data your rental car keeps. Unknown AirTag alert?What the tracker warnings can and cannot do, and the manual check. Found something? Do thisThe order matters: don't touch it, cover your sightlines, document.