Audio Surveillance Equipment

Audio Amplifiers
Learn about audio amplifiers and sound amplification equipment used for surveillance.

Overview of Audio Surveillance Tools

Audio surveillance equipment is used by intelligence agencies, law enforcement, and private investigators to monitor and record subjects in a variety of settings. Audio surveillance can be conducted from a distance using covert listening devices hidden inside the dwelling. Or, devices can be attached to a person inside the house (such as an informant). Also, audio amplifiers can be used to amplify sounds from a distance.

In this article, I’ll review audio amplification systems and digital audio recording devices. In addition, I’ll suggest where you can purchase the equipment.

Audio Amplifier Systems

Audio amplifiers are electronic devices that amplify low-power audio signals (signals composed primarily of frequencies between 20 – 20 000 Hz, the human range of hearing) to a higher level. The amplification equipment can be used either indoors or outdoors to listen to sounds and conversations at a distance.

Audio amplification equipment helps private investigators and police officers to hear conversations that are taking place in a nearby location, such as in another room, or on the other side of the park.

This allows private investigators to listen to what is being said without the other party’s knowledge. The basic point is to be able to hear what is being discussed while remaining unseen. Audio amplification systems can be used for many other purposes, such as eavesdropping on telephone conversations or checking up on what the kids are doing in the backyard.

Targeted Amplification

The amplification devices can be targeted by pointing the unit in the direction of the sounds you are interested in hearing. The particular target could be a person having a conversation with someone else, a person talking on the phone, or multiple individuals have a group discussion. The sounds that are targeted are then amplified as much as 10 times.

What’s Included

The typical equipment that is included with the sound amplification tool includes the listening device, the “sound catching” cone, microphone, mounting clips, batteries, carrying, and storage cases. In addition, some packages include an audio out jack and cables to record conversations. Also, many packages include noise reduction and wind reduction capabilities to help filter out unwanted background noise. This can be helpful when playing back the recording.

Other Uses for Sound Amplification Equipment

In addition to surveillance uses, audio amplifiers can also be used for nature observation, concerts, hunting, bird watching, listening to lectures, personal security, sporting events or even simply watching TV. The listening distance will vary depending on the particular device you are using, but count on being able to pick up conversations from over 300 yards away.

As a protection mechanism, some audio amplifiers come equipped with auto shutoff in case the sound becomes suddenly too loud.

Digital Voice Audio Recorders

Digital audio voice recorders are devices that record sounds, most often used to record voices, in a digital format. The sound files are stored on the device and played back either directly on the device or copied to a computer.

The equipment can be used by almost anyone, including students, attorneys, law enforcement and even private investigators for many purposes. Private investigators can use digital audio voice recorders to record case notes, record witness interviews, and capture voices and sounds as needed during a surveillance mission.

When working as a private eye, you don’t always have the time to stop and write everything down. P.I.’s in old movies and TV shows often pulled out a handheld flip pad to jot down a few notes or facts when working a case. However, modern detectives are always on the go and their hands aren’t always free for writing.

For example, you may be on a long surveillance mission and your hands may be busy working with audio equipment, taking pictures with cameras, or driving a vehicle to follow a subject.

Using a voice recording device will help you capture important notes and set reminders without missing a step, all while keeping your hands free to perform other tasks. Then, when you get back to your office, just replay the notes and transcribe what is meaningful to your PC, tablet or phone.

Voice recorders are great for those times when you don’t have a pen and just need to record some important information. Use a recorder to capture ideas and thoughts on your case, record surveillance notes or set important reminders.

Many of the latest models offer high-quality sound, slim design for easy storage and concealment, one-touch recording and plenty of storage space to keep hours of data. Additional equipment for connecting to a computer or mobile device is often included.

This is one piece of equipment that I recommend for every private investigator, especially those who conduct surveillance and interview witnesses.

Sony Digital Voice Recorder

Sony ICDPX370 Mono Digital Voice Recorder with Built-in USB, Black

This is one piece of equipment that I recommend for every private investigator, especially those who conduct surveillance and interview witnesses.

The recording device has an amazing 57 hour of battery life, so you can spend more time using the recorded and less time charging. In addition, it comes with a handy built-in direct USB connection at the bottom to allow you to quickly and easily transfer audio files to your computer or tablet. 

You can use it to record witness statements, interview conversations, and to record your own case notes. Also, it is small enough to fit secretly in your pocket to record conversations covertly.

Important Note: Be sure to check your state and local laws pertaining to recording witness statements or other spoken statements. It is illegal in most states to record a person’s voice without their consent.

Please note that these tools are not specifically designed or to be used to surreptitiously intercept oral communication. Use for this purpose seriously violates federal laws. Be sure to check your state and local laws before purchasing such equipment and be aware of those laws when using the tools.

The information contained in this article is not intended to condone any unauthorized use of audio amplifiers, such as illegal tapping into other people’s phone conversations. It is the purchaser’s responsibility to comply with all Federal & State privacy rules & regulations.


If you have any questions about audio amplifiers and sound surveillance equipment, please leave a comment below. Or, learn about other types of spy gear and equipment.

Michael Kissiah is the owner of Brandy Lane Publishing, LLC, which owns and operates a small portfolio of websites, including Michael created more than 20 years ago after working as a private investigator in the state of Florida. Since that time, he has become an expert at how to find information online and has written over 1000 articles on topics related to the investigation industry. In addition, he is the author of the "Private Investigator Licensing Handbook", available at



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