Confused about motion sensor types

[Kasuo]

I always get a bit lost between PIR, ultrasonic, microwave, and capacitive sensors. They all seem to detect movement, but I can’t really pin down what makes them different in practice.

[mƎALLEm]

Hello,

Does that question have any relation to any ST product? are you using a specific part number? which one?

Please note that this community is focusing on ST products. Other "generic" questions can be asked in other communities or you can use ChatGPT.

[Andrew Neil]

As @mƎALLEm said, this also doesn't sound like anything to do with ST?

Again, the Arduino forums would probably be a better place to ask such a generic question; eg, their 'General Electronics' forum:

https://forum.arduino.cc/c/other-hardware/general-electronics/21

Other generic forums are also available; eg,

https://electronics.stackexchange.com/

https://www.eevblog.com/forum/ 

Or use your favourite internet search engine - there are lots of resources out there; eg,

https://en.wikipedia.org/wiki/Length_measurement#Transit-time_measurement

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@Kasuo wrote:

They all seem to detect movement, but I can’t really pin down what makes them different in practice.

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Indeed they do - and the difference is given in the name:

• PIR = "Passive InfraRed" - uses infrared light
  https://en.wikipedia.org/wiki/Passive_infrared_sensor;
• ultrasonic - uses ultrasonic sound;
• microwave - uses microwaves
• capacitive - uses electrical capacitance