• Fri. Mar 31st, 2023

Can Ultrasonic Sound Sensors Detect Spirits?

Feb 1, 2023

Lots of people are using certain pieces of equipment fitted with an Ultrasonic Sound Sensor to detect “Spirits”.

This is great in theory, but can an Ultrasonic sensor actually detect a spirit?

Let’s look into this and see if we can find an answer!

How do they work?

Ultrasonic sensors work by pinging a high frequency sound wave (higher than humans can hear, usually between 25 and 50 kHz) from a transmitter, which travels through the air until it hits a physical object, then reflects back to a receiver.

It’s main use is to detect distance and it does this by using a simple formula:

r = 0.5 x T x C

where r = distance, T = time and C = speed (the speed of sound is 343 m/s). We multiply by 0.5 (or we could divide by 2, it’s both the same) because in this instance we only want to work out the distance to the object, not the distance to the object and back to the receiver.

Copyright © 2005 Georg Wiora – Wikimedia Commons URL

This is how bats “see” in the dark!

In order for this to work properly then the angle of the reflecting surface has to be correct in order to bounce the wave back towards the receiver. If the wave does not bounce back at the correct angle then the wave will simply miss the receiver. The reflecting surface also has to be a physical object!


When the device calibrates, you need to point it towards a physical hard surface (soft objects absorb sound) at the correct angle. It should be flat (or perpendicular) to the device. You also need to take into consideration the angle of the acoustic beam and the maximum length the sound can travel, which is usually around 5 meters for these types of ultrasonic sensor.

If the device is pointing at a 45 degree angle towards a wall, then the projected sound wave is not going to travel back to the receiver on the device. It will reflect off the surface and go in the wrong direction.

Wrong angle position

Source: Macduino

The device then works out how far away the “control” distance is and sets that to its default distance. Then if anything paces between the control surface and the sensor, the new distance will trigger the device.

What Can / Can’t an Ultrasonic Sensor Detect?

Ultra sonic sensor are not affected by gas, smoke, dust or other air born particles, even some ultrasonic sensors can work under water!

Therefore, if a spirit is stood in front of an ultrasonic sensor (you know, the type of spirit that you cannot physically see), would the sound wave reflect off the spirit? – I don’t see how this is possible.

Even if you could see the spirit as an apparition (the type of see through wispy fog), since the sensor is not affected by smoke, gas, dust or air born particles, how could the sensor detect it? – I got a friend to blow vape smoke over an ultrasonic sensor and it didn’t detect it.

But it can detect glass, which is transparent, so how does that work?

Glass is transparent, but it is still a physical object with a solid surface. When it comes to sound waves, physical objects that are transparent work exactly the same as physical objects that are not transparent.

Transparent objects allow light waves to travel through them, but because glass has a physical surface then sound waves will reflect off it.


At this moment in time, I am not convinced that ultrasonic sensors can detect spirits! Purely because of how the sound wave works and what does not affect it.

But I will keep researching into this…

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