The Simple Tech Behind Hidden Camera Detectors

January 12, 2024 by 26 Comments

If you’ve ever been concerned about privacy in a rental space or hotel room, you might have considered trying one of the many “spy camera detectors” sold online. In the video after break [Big Clive], tears one down and gives us  an in-depth look at how these gadgets actually work, and their limitations.

Most detector follow the same basic design: a ring of LEDs through which the user inspects a room, looking for reflections indicating a potential hidden camera. Although this device can help spot a camera, it’s not entirely foolproof. The work best when you’re close to the center of a camera’s field of view, and some other objects, like large LEDs can produce similar reflections

The model examined in this video takes things one step further by adding a disc of dichroic glass. Coated with a metallization layer close to the wavelength of the LEDs, it effectively acts a bandpass filter, reducing reflections from other light sources. [Big Clive] also does his customary reverse-engineering of the circuit, which is just a simple flasher powered by USB-C.

[Big Clive]’s teardowns are always an educational experience, like we’ve seen in his videos on LED bulb circuits and a fake CO2 sensor.

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Hackaday Podcast 134: Hackers Camping, Metal Detecting, 360° Hearing, And Pocket Computing

September 3, 2021 by 1 Comment

Hackaday editors Elliot Williams and Mike Szczys are joined by contributing editor Jenny List to talk about her adventure at Born Hack last week. We also discuss the many capacitor values that go into regen receivers, the quest for a Raspberry Pi handheld that includes a slide-out keyboard, and how capacitive touch might make mice (mouses?) and touchpads better. There’s a deep dive into 3D printer bed leveling, a junk-box metal detector build, and an ambisonic microphone which can listen any-which-way.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

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Random Numbers From A Smoke Detector

June 26, 2021 by 21 Comments

The quest for truly random numbers is something to which scientists and engineers have devoted a lot of time and effort. The trick is to find an unpredictable source of naturally occurring noise that can be sampled, so they have looked towards noisy gas discharge tubes or semiconductor junctions, and radioactive decay. Noisy electrical circuits have appeared in these pages before as random number generators, but we’d be forgiven for thinking that radioactive decay might involve something a little less run-of-the-mill. In fact we all probably have just such a device in our houses, in the form of the ionisation chamber that’s part of most household smoke detectors. [Lukas Koch] has built a project that shows us just how this can be done.

A smoke detector of this type uses a metal shell to house a tiny sample of radioactive americium that emits alpha particles into the space between two electrodes. These ionise the air in that space, and the detectable effect on the space between the two electrodes is increased when ionised gasses from smoke are present. However it can also quite happily detect the ionisation from individual alpha particles, which means that it’s perfect as a source of random noise. A sensitive current amplifier requires significant shielding to avoid the device merely becoming a source of mains hum, and to that end he’s achieved a working breadboard prototype.

This is still a work in progress and though it has as yet no schematic he promises us that it will arrive in due course. It’s a project that’s definitely worth watching, because despite getting more up-close and personal than most of us have with radioactive components, it’s one we’re genuinely interested to see come to fruition.

Of course, we’ve seen smoke detectors in more detail before here at Hackaday.

Arduino And Wire Detects Metal

October 21, 2020 by 7 Comments

Our old math teacher famously said, “You have to take what you know and use it find what you don’t know.” The same holds true for a lot of microcontroller designs including [rgco’s] clever metal detector that uses very little other than an Arduino. The principle of operation is simple. An Arduino can measure time, a coil and a resistor will create a delay proportional to the circuit values, and metal around the coil will change the coil’s inductance. As the inductance changes, so does the delay and, thus, the Arduino can sense metal, as you can see in the video below.

The simple principle is also simple in practice. Besides the Arduino and the coil, there’s a single resistor. You want a small coil since larger coils won’t detect smaller objects. If you don’t want to wind your own coil, [rgco] suggests using a roll of hookup wire as long as the resistance is under 10 ohms.

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Teardown: Cobra XRS 9740 Radar Detector

March 18, 2020 by 46 Comments

Drivers with a lead foot more often than not have Waze open on their phone so they can see if other drivers have spotted cops up ahead. But avoiding a speeding ticket used to involve a lot more hardware than software. Back before the smartphone revolution, that same driver would have had a radar detector on their dashboard. That’s not to say the gadgets are completely unused today, but between their relatively high cost (one of the top rated models on Amazon as of this writing costs over $300) and the inevitable false positives from so many vehicles on the road having their own radar and LIDAR systems, they’ve certainly become a less common sight over the years

The subject of today’s teardown is a perfect example of “Peak Radar Detector”. Manufactured back in 2007, the Cobra XRS 9740 would have been a fairly mid-range entry offering the sort of features that would have been desirable at the time. Over a decade ago, having an alphanumeric display, voice alerts, and a digital compass were all things worth shouting about on the box the thing was sold in. Though looking like some kind of Cardassian warship was apparently just an added bonus.

As the name implies these devices are primarily for detecting radar activity, but by this point they’d also been expanded to pick up infrared lasers and the strobe beacons on emergency vehicles. But false positives were always a problem, so the device allows the user to select which signals it should be on the lookout for. If you were getting some kind of interference that convinced the detector it was being bombarded with IR lasers, you could just turn that function off without having to pull the plug entirely.

But it’s important to remember that this device was built back when people were still unironically carrying around flip phones. Detecting laser and multi-band radars might sound like something pulled from the spec sheet of a stealth fighter jet, but this is still a piece of consumer electronics from more than a decade in the past. So let’s crack it open and take a look at what goes on inside a radar detector that’s only a few years away from being old enough to get its own driver’s license.

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Drone + Ground Penetrating Radar = Mine Detector?

October 12, 2018 by 30 Comments

Most civilized nations ban the use of landmines because they kill indiscriminately, and for years after they are planted. However, they are still used in many places around the world, and people are still left trying to find better ways to find and remove them. This group is looking at an interesting new approach: using ground-penetrating radar from a drone [PDF link]. The idea is that you send out a radio signal, which penetrates into the ground and bounces off any objects in there. By analyzing the reflected signal, so the theory goes, you can see objects underground. Of course, it gets a bit more complicated than that (especially when signals get reflected by the surface and other objects), but it’s a well-established technique even though this is the first time we’ve seen it mounted on a drone. It’s a great idea: the drone allows you to have the transmitting and receiving antennas separated with both mounted on pole extensions, meaning that the radio platform can move. Combined with a pre-planned flight, and we’re looking at a system that can fly over an area, scan what is under the ground, and store the data for analysis.

[Via RTL-SDR]

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An Introduction To Storm Detector Modules

March 22, 2018 by 41 Comments

Lightning storm detectors have been around for a surprisingly long time. The early designs consisted of a pair of metal bells and a pendulum. When there was a charge applied, for example by connecting one bell to the ground and the other to a lightning rod, the bells would ring when a lightning storm was close by. In the mid 18th century, these devices were only practical for demonstration and research purposes, but very likely represent the earliest devices that convert electrostatic charge to mechanical force. A bit over a hundred years later, the first lightning detector was considered by some as the first radio receiver as well.

As soon as I found out about storm detector chips, I knew I would have to get one working. For about $25, I ordered an AMS AS3935 module from China. This chip has been featured before in a number of excellent projects such as Twittering lightning detectors, and networks of Sub-Saharan weather stations. While there’s an Arduino library for interfacing with this IC, I’m going to be connecting it up to an ESP8266 running the NodeMCU firware, which means digging into the datasheet and writing some SPI code. If any of the above tickles your fancy, read on! Continue reading “An Introduction To Storm Detector Modules” →