Cable Sensor Circuit Detects SMPS Faulty of PC Accidentally

Building this nice simple yet practical circuit saved me alot. Okay, i got this
circuit design from multiple of websites and i built mine.
a. https://www.instructables.com/Invisible-Broken-Wire-Detector/
b. https://www.instructables.com/Wireless-AC-Current-Detector/

Circuit drawn with easyeda

Result

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Video

After successful built it is time to test, i moved the detector to nearby cable,
plug the cable and switch On, voila works like charm! Then click switch Off
the detector Led would still On but dimmer... After troubleshooting  circuit
just works fine with other cable that is not in switches-hub i tested earlier.

Weird? i started to plugged off all cables one by one, until i unplugged PC' 
power cable. The detector Led stop completely... Nah! i now there is something

going on during the SMPS of my PC got plug in. It is still `On` and drawing some

electric actively and silently.

Lesson learned, by now i unplugged home-appliances that no longer being used ^^.