Sniffing Out Microphones and Other Bugging Devices Yourself

Understanding the Behaviour of Sound

In this article, I will attempt to show you how to detect transmitters, bugs and other miniature microphone devices that may have been inserted in your own house or office. Let us first understand the dynamics of sound. Sound always takes the path of least resistance, such as a doorway, duct or open window. If someone wants to spy on you, he / she may most likely have placed their bugs in overlooked air paths such as over, under or around doors. Sometimes you can find holes in walls, or spaces around pipes and wiring. Remember even the smallest air path can transmit sound to a microphone.

Sound-as well as electrical signals-travels along the metal surfaces of electrical conduits, pipes and ducts. You can recover this sound after it has traveled more than 100 feet in this manner. Water-filled pipes transmit sound with much less distortion than empty pipes.

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Sounds, depending on their frequencies, penetrate floors, ceilings and doors. After sound energy hits a structure, some reflects from the surface, some is absorbed and the rest passes on. Remember even a so-called “soundproof’ room can be bugged by your enemies especially if the soundproofing consists of acoustical tile. Truth is, acoustical tile can actually reduce a room’s sound security. Acoustical tile was made to reduce sound reverberations in a recording studio. Tile lets walls absorb more sound, reducing its level in the room. Sound that is absorbed is not lost because energy cannot be destroyed, only converted. Therefore, acoustical tile may reduce a room’s security by allowing sound to be transmitted through the wall structure and it is often applied in a hanging configuration allowing space to place surveillance gear above the tile.

Most microphones will “hear” through acoustical tile quite well, if not simply punch a small hole with a nail or dentists drill. A small camera can also be placed behind these tiles because the tiny holes on the acoustical walls can easily relay video information to your enemies.

Distortion and Interference

Sound waves not only travel from their source, they also are reflected when they hit a surface. Reflected sounds behave as if the surface they hit is their original source, and can be reflected again. Sound patterns become very complicated after reflecting and re-reflecting from ceilings, floors, walls and internal objects. Reflected sound waves can merge almost exactly with sounds arriving from the first source. Sounds merged like this have an increased sound level and are “in phase.”Sound is distorted when a disruption changes its normally smooth pattern. Distortion may be encountered before the sound is recorded, during the recording or at playback. Excessive distortion cuts down the recovery and understanding of intercepted sound. Which is why your enemies will take great care to place their bugs in distortion-free places only. When placing the microphone, they will consider how quickly sound loses power after leaving its source. Say your friend is talking to you from 10 feet away. If you then stand 20 feet apart, the magnitude of his voice doesn’t become one-half as loud-it cuts to one-fourth! The magnitude of sound declines according to the inverse square law. If you quadruple the distance between you and your friend, the power of the sound of his voice drops to one-sixteenth. In surveillance work we are interested in two kinds of sound: Sounds (usually voices) we want to hear, and all other unwanted sounds no matter what their origin. Types of sound interference are countless. Rain, plumbing, air conditioning, fans, traffic, planes and trains are just some of the problems. When you are being monitored, just one more person speaking in the near vicinity can cause massive interference.

Sometimes original and reflected sound waves meet so that their decompressions and compressions neutralize each other. When they merge this way the sounds are “out of phase.” If neutralization is perfect, the effect is called cancellation. Sounds are rarely totally out of phase, so the nullification effect is usually just called interference.

Bugging Rule No. 1 – Place mics Close

best bug sweeping experts indiaWhether hard wiring, stashing a recorder or placing a transmitter, the prime rule of your enemies will be: place the microphone as close as possible to the people speaking. The average male’s speaking voice falls between a frequency range of 100 Hz and 8 KHz and the average female’s between 200 Hz and 10KHz. Most speech falls between 600 Hz and 4 KHz. You can sharply reduce interference without sacrificing clarity and understanding by reducing the power of frequencies between 600 Hz and 4 KHz. Some recording systems come with low pass and high pass filters that limit the band pass to achieve this reduction, automatically reducing sounds outside of the voice range. Early telephones did this by virtue of their carbon microphone construction. Rooms constructed with hard surface walls and containing filing cabinets, desks and other such furnishings are known as “hard rooms.” Hard rooms reflect sound waves a great deal, creating a feeling of loudness despite a lack of loud sounds. On the other hand, “soft rooms” are fitted with acoustical tiles, soft. walls, padded furniture, drapes and carpets. Soft rooms absorb sounds and cause a feeling of quiet regardless of the presence of loud sounds.

Soft rooms pose fewer surveillance problems than do hard rooms. Hard rooms reflect sound more, causing distortion. By its construction, a hard room’s structure multiplies the effects of disturbances and interference. If your enemy has had the time and opportunity chances are that he would have tested several spots in the target room to find the one with the least amount of annoying distortion. Some operatives take a surreptitious photo of the room on an earlier reconnaissance visit and then pre-plan the actual placement by experience or by experimenting with a similar room. This is often possible if the target room is a motel room or apartment with duplicates nearby.


If you are being bugged, chances are that your enemies have placed the mic as close as possible to where the talking will take place. They will avoid that will cause the microphone to pick up too many reflected sounds. For instance, placing a microphone in a file cabinet, or metal waste paper basket could add echoes that would make any received speech incomprehensible. Besides finding a good location to hide the microphone, they would have also checked for and tried to remove any sources of electrical interference. Sources that cannot be removed require diligent placement of both cabling and the actual microphone.

Electrical hum comes from motors, transformers, SCR dimmers and electrical wires. Many appliances cause hum and noise. So the microphone cables would be placed away from these sources of hum. The best places to conceal a microphone are those above a standing person’s eye level or below a seated person’s. People do not often scrutinize these areas. Your enemies will also take advantage of any obstructions where one can stash a microphone behind. Even though doors, ceilings, walls and floors are many times hollow, they seem solid and people imagine them to be free of suspicion. A pro snooper will usually placed microphones inside these supposedly solid locations. Walls also have the added advantage of nearby wiring with which to power the transmitter through which your conversations are being heard and recorded. A tiny hole can be drilled for the microphone, or existing holes such as those in electrical sockets can be utilized for sound gathering. Ceilings also offer benefits when concealing microphones. Crawl spaces and attics can give room in which to work. Outlets, fixtures and ducts are good places for a microphone, provided there is no acoustical and electrical interference.

So if you fear that you are being bugged, apart from looking at all the nooks and crannies above standing eye level and below seated level, also check the walls and ceilings of your house which ultimately is the most difficult and time consuming and most often requiring expert bug-sniffing hardware. Call us on +91 98206 07875 for specialised help however small or large the suspected area maybe. We have the best Spectrum Analyzers, Audio Amplifiers and Non Linear Junction Detectors to sniff out bugging devices.

Author Bio

Amit Sen, a commercial pilot by training, has over 15 years experience in the space of corporate investigations, handling Copyright & Trademark infringement cases, Pre – employment verification Industrial Espionage investigations, Asset & Net – Worth assessment assignments and vendor / supplier verification cases, among others. Co-founder of Alliance One – who are the best de bugging and espionage detectives in India. Amit has also successfully completed assignments in a wide range of sectors, including the machine tools industry, pharmaceutical industry, hospitality sector, specialized equipment (Oil & natural gas sector, aviation industry etc.), telecom industry & the IT & ITes sectors. These cases have all involved both offline and online investigations.

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