Hidden camera lenses are coated in glass with a specific property: they retroreflect light
back toward its source. When your phone's flashlight illuminates a room, a concealed camera
lens will glow with a bright, distinctive dot — while everything else scatters light
in all directions. This is how professional counter-surveillance sweeps work, and your phone
already has everything needed.
Hidden cameras are found in Airbnbs, hotel rooms, and changing rooms every week.
In 2019, a couple in South Korea found 1,600 guests had been livestreamed from hidden cameras
in motels. In 2023, a camera disguised as a smoke detector in an Irish Airbnb recorded guests
for months. The retroreflector effect is real — security researchers and law enforcement have
used phone camera + flashlight to find covert cameras for years.
How to sweep a room: 1. Turn off all lights so the room is as dark as possible.
2. Press start — this activates the rear camera and flash.
3. Slowly pan the camera around the room, looking at the live view.
4. Any hidden camera lens will appear as a bright, twinkling or glowing dot that doesn't look like a reflection from flat surfaces.
What to look for: The overlay highlights bright isolated spots in the frame.
Retroreflectors appear as pinpoints much brighter than surrounding surfaces — often with a slight
colour tinge (red/orange from lens coating). Check air vents, smoke detectors, clocks, USB chargers, and picture frames.
0
bright spots detected
waiting for camera
—max brightness
—hot spots
—threshold
spots
—
max px
—
▶ the physics of retroreflection
A retroreflector sends light back toward exactly the source direction, regardless of the
angle of incidence. Camera lenses achieve this unintentionally: the convex front element
focuses incoming light to a point, which then bounces off the sensor (or an internal reflective
element) and retraces the same path out. From the camera's perspective, the lens appears as
a very bright, directional point source.
This effect is maximised when your light source and camera are at nearly the same position —
which is exactly the case when you use a phone's rear flash and rear camera together.
Professional RF detectors and lens detectors exploit the same physics at longer range using
laser illuminators and polarised optics.
Limitations of this browser approach: we can't control flash timing precisely, so we look for
statistically bright isolated pixels rather than true retroreflector signatures. Real covert
camera lenses are typically 3–8mm in diameter and appear as isolated bright pinpoints, distinct
from the smeared reflections you get from flat surfaces like glass or mirrors.