Can drones hear conversations? [The surprising science]

Privacy is a very important component of flying a drone. If you are in an area where there are drones flying regularly you may wonder if drones can actually hear your conversations. I know that when I was first flying my drone I was amazed at the volume of the sound it makes while it is flying. Surely this is enough to drown out even the loudest of conversations? Well, in this article we can go over everything you need to know about whether or not drones can hear conversations and what you can do to protect yourself.

It is unlikely that consumer drones are able to hear your conversations as most of them do not carry microphones. However, with special microphones and audio software drones are able to listen in on your conversations.

Most drones do not come with a built in microphone. When I bought my DJI Mavic air, my first ever drone, I was surprised that the audio was only able to be collected and recorded through the DJI app.

However, there are some drones which can pick up sounds and there are third-party accessories and hardware which drones can carry to record audio during their flight.

Can drones pick up sound?

Most of the consumer drones available on the market are not able to record sounds. The biggest hurdle that is stopping drones from recording sounds is quite literally how loud they are.

Drones are incredibly noisy due to the high propeller rotation frequency combined with the amount of air that they are required to force downwards in order to stay in flight.

If you were to simply put a microphone on a drone it is likely that the microphone will pick up to main sounds which would wash out anything that could be heard in the distance.

Those sounds are the electric noise generated by the motors and the sound of the propellers moving air across the surface of the microphone.

In order to add reliable and useful recording capabilities to a drone you need to add an external shot gun microphone which is able to remove all of the background noise generated by the drone and is on the long arm so that it is far away from the turbulent air produced by the propellers.

Such a microphone has been developed by a company called Dotterel.

Dotterel is a company that develops noise reduction and audio recording technology for unmanned aerial vehicles.

They have created an aerial audio microphone which can be carried by a drone and can be used for emergency services, defence, and TV or film. You can also have live one-to-one conversations when using a speaker on the drone.

A full rundown on this technology is shown in the YouTube video, below. I think you’ll be amazed at how clear the is despite being attached to a drone.

Audio through an app

If you have watched a load of YouTube videos of people talking to their drones it is likely that that audio is recorded separately from the drone. It is typically captured through a lapel microphone which is plugged into the pilots phone or into an external audio recording device such as the H4n Zoom recorder.

This is the best approach for getting crystal-clear audio while you are flying your drone.

The science to pick out speech from a drone

In 2018 there was an article published which talk about how to reduce reduction for audio captured by drones. This shows us that there is a fair amount of interest in adding microphones to drones since they are able to use drones in surveillance, broadcasting, and other security applications.

The scientists were able to reduce the noise of the audio by using a combination of active noise control and spectral subtraction methods. Their results showed that the proposed technique can produce a speech signal without too 67.5% similarity to the original signal. This method of combining two processes outperformed active noise control and spectral subtraction by a significant amount.

Can drones hear conversations? Science
Result of recording from a drone using active noise control and the hybrid noise reduction. You can see that the speech is much closer to the hybrid noise reduction trace.

Besides using software to minimise the noise and sticking the microphone on a large boom away from the drone the other option for picking out a conversation with a drone is to actively reduce the noise the drone makes.

The same company that produced the microphone is also producing passive noise reduction shrouds to make the drones quieter.

Passive noise reduction

The same company mentioned above, Dotterel, has produced noise reduction and safety shrouds for propellers. They reduce the noise that is created through the complex interaction of the blades with the body, arms and body of the drone. A safety shroud firstly reduces the noise by the propeller by absorbing the sound and then reflects any residual noise up and away from people that are on the ground below. There are specific frequencies absorbed in the core as it is made of acoustic materials that absorb some frequencies.

The shrouds can be retrofitted to nearly any drone manufacturer but must be specific to the drone that you are using. This company is currently working with customers, external researchers and academic institutions to stay at the forefront of noise reduction technology for drones.

If you want to know more about how you can make your drone quieter check out my other article which goes into this question in much more detail.

How can I make my drone quieter

Some other ways that you can reduce the noise of the drone are:

  • use more rotors – using more rotors on a drone means that each motor is operating at a lower power. More propellers means that each aircraft motor can operate at a slightly different number of revolutions per minute. This means that the generation of similar harmonics that produce the drone sound can be spread across many frequencies reducing the sound of the drone.
  • Using a slower propellers – using larger propellers means that the propeller can move slower to displace the same amount of air. Increasing the diameter of the propellers will increase their thrust factor and create a greater vertical push. Slowing down the propeller will also make the frequency of the noise much lower.
  • Sanding down the surface of the propellers – making sure that your drone propellers are as smooth as possible and free from bumps from manufacturing can reduce the sound volume and quality.
  • Low noise propellers – you can purchase low noise propellers which can significantly change the volume of the noise by reducing the number of revolutions per minute the blades make and also having a very smooth surface they can reduce the noise by about 3.5 dB.

Using these techniques make it much more likely that a drone is able to record a conversation. However, the drone has to get relatively close to you which means that the drone will be very obvious as it is recording your conversation.

Can drones hear inside your house?

In order for a drone to be able to hear inside your house the audio and sound waves need to escape from your house. Not only do they need to escape from your house but they also need to be at a high enough volume that it is able to be recorded over the noise generated from the drone. As we talked about, above, this is a problem unless you have a specific shot gun microphone mounted far away from the down wash created by the drones propellers.

Drones collect primarily visual data and there is the potential that even the smallest vibrations can be turned into audio as demonstrated by MIT’s 2014 study which was able to extract speech from the vibrations of a potato chip bag filmed through soundproof glass.

They were also able to create audio by looking at the tiny vibrations generated on a leaf in the same room as someone who was talking.

You can view this for yourself in the YouTube video, below.

By detecting the minute vibrations of objects they are able to recover intelligible speech from approximately 15 feet away.

At 15 feet it is likely that you will be very aware of the drones presence and the small vibrations caused by the drones flight will likely not be able to be separated from the vibrations of leaves or objects vibrating in the area due to sound.

How to protect yourself against drone recordings

In 2016 a drone advisory committee was established and they released a set of best practices and guidelines for respecting people’s privacy when flying a drone.

Even though these best practices are common sense and can be very effective at protecting people’s privacy they are completely voluntary and rely on the drone pilot doing the right thing. It is very hard to police drone regulations since drones are able to be flown away from law enforcement very quickly.

Therefore, even though most drone pilots are striving to do the right thing most of the time there are some which will not fly in line with the local laws and regulations.

Here are some of the ways that you can protect yourself from being spied on by a drone and having your conversation recorded. Remember, that it is actually very unlikely that the drone is recording your conversation or even able to detect your identity from a significant distance away.

If you want to know more about how far drone cameras can see I calculated the detection, classification and recognition distances for a range of cameras and resolutions. You can check out the full article – click here.

How far can drone cameras see?

The good news is that it is very obvious when a drone is at a distance where it can record your conversation. Typically the telling signs are that you can hear the drone clearly and you are aware of its presence and you may even be able to spot it by looking in the direction of the sound.

There are also a range of drone detection apps which can be used to tell if a drone is spying on you. The drone watcher app turns your android device into a detector of drones and is able to alert you and track their path. The app detects most commercially available consumer and prosumer drones and records the data including the drone type and ID which can be used to document evidence to be used by local law enforcement.

Here are some of the best ways to make sure that a drone is not able to identify you or hear your conversation.

Get further away from the drone

Firstly, I recommend that if you are concerned about a drone recording your conversation you should move further away from the drone. Even though drone cameras are very advanced the detection limits of microphone mean that even the smallest increase of distance can result in intelligible audio recording.

Move out of line of sight

Moving out of the line of sight of the drone will also be one of the best ways that you can be confident that the drone cannot see you and it cannot hear you.

Drones rely on direct line of sight with the pilot for high resolution streaming of the footage and also rely on line of sight to spy on people. By simply moving to an area that is undercover or out of the line of sight of the drone you will be able to escape any recording whether it is a video or audio.

Talk in noisy urban environments

If you are suspicious that a drone is recording your conversations the first thing that you can do is decide to meet in noisy urban locations which contain a lot of background noise.

Noisy urban environments include a lot of car noise, construction noise, traffic and other pedestrian noise. This is a very effective way of masking your conversation from anyone who is trying to record it. They will need a very high-powered shot gun microphone in order to resolve your conversation from the background noise.

Report the drone

One of the most effective ways of avoiding drones spying on you and your conversation is by reporting them to the police. Take a note of the location, type of drone, and time of the incident so that the police can follow up with their investigations on the drone pilot and investigate any wrongdoings.

Most drone pilots always tried to do the best thing but there are a few which break the local laws in order to capture incredible shots and footage of which your conversation may become collateral damage.

Summary

In this article, we have gone over all of the ways in which drones may be to hear your conversation. Luckily, most commercial drones are not fitted with a microphone. However, if you do attach a microphone to the body of a drone the recording is likely to be completely unusable due to the noise of the drone itself (the motors and down wash).

There are a few companies which are attaching microphones to the drones on a long boom arm but these are very obvious and still have to get relatively close to a conversation to record it properly.

Your conversation is safe from drone recordings at the moment and it is likely that you will spot the drone well before it is able to pick up any of your conversation.

The Author

Dr Andrew Stapleton is a writer and YouTuber with a PhD in science. He has written and/or produced videos for Science Alert, COSMOS magazine, and Australia's Science Channel among others. Andy started droneflyingpro.com to share his love and the research of all things drone! He has been a drone pilot for many years and has flown many types of drone. His favorite is still the DJI Mavic Air for the portability and functionality packed into a small and portable drone!