Detection methods

However small a pinhole camera is, its lens is a piece of glass that reflects light. This is what Shutterguard relies on most.

Photo mode (free)

The app takes one photo with the flash on and one with it off and compares them. Ordinary surfaces brighten evenly, while a small round reflection like a lens stands out in the difference. These rules then filter out common false alarms:

• Shape: only roughly round spots of a plausible size are kept, so long reflections from window frames or table edges are dropped.
• Brightness: if the scene is too bright, the scan pauses and asks you to turn off the lights or close the curtains.
• Angles: you are asked to shoot again from another angle. A spot that stays put after a large change of angle behaves more like a mirror or metal, so its score is lowered.
• Self‑lit spots: anything already glowing with the flash off (indicator lights, screens) is not a reflection and is heavily discounted.
• Color: the flash is white, so clearly red, green or blue reflections (colored LEDs, reflective stickers) are slightly discounted.
• Actual size: iPhones with LiDAR measure the real size of each spot. Anything wider than about 2 cm cannot be a pinhole lens (it is usually a metal bowl or a lampshade) and is discounted. This applies to both the free version and Pro.

Sweep mode (Pro)

The flash blinks quickly in an irregular pattern for about 5 seconds per pass while you move the phone slowly around the room. Only spots whose brightness follows that exact pattern become candidates, so room lights and screens drop out on their own. When a candidate appears, the app guides you to move closer and hold steady for a 5‑second check, and each spot ends up with one of these results:

• Confirmed: lens‑like (red frame): strong sync, and both its appearance and real size fit a lens.
• Synced spot, unconfirmed (yellow frame): it follows the pattern but other signals are weak, so it is scored conservatively.
• Move closer and check again: too far away to measure reliably. The evidence is kept without a verdict; scan again from about 30 cm.
• Ruled out (green frame): too large for a pinhole, a mirror reflection or the wrong appearance. Not scored.

Many hidden cameras have night vision and give off infrared light (850 or 940 nm) that the eye cannot see. The front camera filters infrared less strongly, so in a dark room, point it at a suspicious object and move slowly: the infrared light shows up as a bright dot, and the phone vibrates when it finds one.

A dot that blinks on and off regularly looks most like intermittent infrared lighting and scores highest; a steady dot comes next; a brief flash is treated most cautiously.

Limits

It only finds cameras that are emitting infrared at that moment. In daylight, with the lights on, or with night vision off, there is nothing to see. Front‑camera sensitivity also varies by model.

The app scans nearby Bluetooth devices and uses signal strength plus publicly broadcast details such as the device name and manufacturer ID to flag devices within about 2 m that don't look like earbuds, watches, phones or other common products. Closer devices score higher. Devices that always live in your own home can be marked as "My environment" so they are no longer scored.

Limits

iOS does not give apps a device's real MAC address, and classic Bluetooth devices such as speakers and car kits can only be scanned by the system itself. Cameras with Bluetooth off, or without Bluetooth at all, are invisible to this method.

On the Wi‑Fi network the phone is connected to, the app asks whether any device offers the video streaming services cameras typically use, or has a name containing words such as cam or ipcam. It only sends standard service queries; it never connects to a device or transfers content.

Limits

iOS does not let apps scan Wi‑Fi networks they are not connected to, so cameras on their own hotspot or mobile data are completely invisible. In testing, some cameras only joined the network while their owner had the camera's app open. Results may also include a venue's own security cameras, printers and other legitimate devices.

The microphone listens to high frequencies people cannot hear (about 17 to 22 kHz). It records the background level for the first 3 seconds, then logs an event when that band rises sharply for more than 0.8 seconds. It only runs during a scan and never records, saves or uploads audio.

Limits

It cannot detect GSM, 4G or FM wireless bugs, which need a professional RF detector. Fluorescent lights, switches and fridge compressors can also set it off, so false alarms are common.

The magnetometer (compass sensor) records the room's magnetic field and logs large changes. Powered cameras create weak magnetic fields, but in testing almost every indoor appliance and metal structure set it off, so since August 2026 the magnetic field no longer counts toward the score and is shown only as environment information.

The magnetic field is only useful within about 5 to 10 cm. The scan screen offers a close‑range magnetic check: set a baseline in mid‑air, then slowly slide the top edge of the phone along a suspicious object. The larger the change, the denser the vibration. It suits a second check of a single spot.