Is that motion sensor in the corner really a camera?

What a real PIR sensor window looks like

The white or milky window on a real motion sensor is a Fresnel lens. It is a sheet of plastic molded into rings or rows of small facets, like a flattened honeycomb or a set of ridges. You can often see the pattern if you shine a light across it at a low angle. It is cloudy, not clear, and there is no single dark dot at its center. Behind it sits a small heat sensor, which you usually cannot see through the plastic.

A camera lens is different. It is a small round piece of glass, often 1 to 3 mm across, with a dark center and a sharp edge. In a camera version it is placed either in a clear or tinted spot on the dome, or in a separate hole on the body just under the dome. If the window is clear enough to see a round dark lens through, or has one hole that breaks the facet pattern, that is not how PIR sensors are built.

Clues around the sensor

• No alarm panel in the home. A motion sensor reports to an alarm control panel or hub, usually near the front door. In a rental with no keypad, no hub and no alarm stickers, a lone motion sensor has nothing to talk to.
• A sensor in a bedroom or bathroom only. Alarm installers cover hallways and entry points. A single sensor pointed at a bed, with none in the hall, is placed for a view.
• A USB cable running down the wall. Most wireless alarm sensors run for years on a small battery, and wired ones use thin alarm cable hidden in the wall.
• A small red or blue light that never changes. Real sensors often flash briefly when they detect you walking past. A light that stays on steadily, or none at all, is less typical.
• It does not react to motion. Wave at a real sensor with a test light and it blinks; a camera shell may do nothing.

Which Candor check fits a motion sensor

The lens finder is the main tool. A Fresnel lens is cloudy plastic, so it scatters flashlight into a soft glow across the whole window. A glass camera lens throws back one small, sharp point. That contrast makes motion sensors easier to judge than many objects. Hold steady from below and watch for a pinpoint that stays fixed while the rest of the dome glows evenly.

Use the infrared check with the room dark. Many camera versions have night vision LEDs around the lens, and your front camera can often show them as a faint purple glow. A real PIR sensor does not emit infrared light; it only receives it.

The Wi-Fi camera scan can flag a sensor camera that streams to an app, if you are on the same network. Real smart-home sensors join Wi-Fi too, but they do not offer a video stream. The magnetic sensor is of little help, since both real and fake sensors hold electronics, and the unit is usually out of reach.

Handling a suspicious sensor safely

Do not climb furniture to pull a sensor off a high wall. Cover it with a piece of tape or a sticky note on the window if you can reach from a stable step, and photograph it from below. If the home has an alarm system, ask the host or landlord which sensors belong to it. In a vacation rental, a motion-sensing camera indoors breaks many platform rules; the Airbnb guide explains how to report it.

Check a corner motion sensor from the floor

1. Look for the rest of the alarm systemBefore you check the sensor itself, find the alarm keypad or hub. Check the front door area, a hall closet and the kitchen wall. Note if there is none.
2. Study the window patternShine a light across the white window at a low angle. A real sensor shows even rings or facets. Look for a round dark spot or a clear patch that breaks the pattern.
3. Run the lens finderDarken the room and open the lens finder in Candor. Stand under the sensor, then step back two or three meters. A small sharp point that holds still while the dome glows around it is the thing to look for.
4. Check for infraredSwitch to the infrared check with the front camera and point it at the sensor in the dark. A purple or white glow means it emits infrared light, which a real PIR sensor does not.
5. Walk past itWalk across the room in front of the sensor. A real alarm sensor often flashes a small light the first time. Note whether it reacts at all.
6. Ask, cover and reportAsk the owner which sensors belong to the alarm. If the answers do not match what you see, cover the window, take photos and report it.

Frequently asked questions