You can tell the guy probably doesn’t know what he’s talking about from the beginning when he says “110”.
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I’m going to ask the dumb question. Why does it light up before it’s inserted into the outlet?
Those tools sence voltage and don’t need to be in contact with a power source to activate if the voltage is high enough.
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You can try it yourself to see what I mean, start your clothes dryer and put the instrument up to the power cable. You only have to get close for it to light up.
I agree Chris, no one should ever say 110 ever again. It’s 120 volts, that’s the nominal voltage used in the US.
You mean like this:
The sniffer is capacitively coupled to the “hot” wire in the outlet. This is the only outlet in my house that does it. Two things to note are : the outlet is ungrounded and it is a metal box.
The scientific reason is beyond me, but it only happens with ungrounded outlets. So it must have something to do with the coupling of the outlet wiring and sniffer.
I will add, LOL it is more than 110v. You guessed it 120. 
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Before inserting into a ‘normal’ outlet as an example, he claims that the “Widow Maker” MUST be inserted all the way into the outlet before it will sound or light… leading up to the MAJOR PROBLEM at the other outlet!!
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Guess I need to get on FB and find this video. Could use a good laugh…
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The service entrance to my house. Not touching any cables, sencing through the conduit. I think in your case Marcel, the metal box may have something to do with it. I have been told they activate because of the magnetic field produced by the electricity. They tend to beep when you tap your fingers on the tip also.
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Here’s a good article from the wizards at Fluke:
https://www.fluke.com/en-us/learn/blog/electrical/understanding-capacitive-voltage-sensors#:~:text=The%20capacitive%20voltage%20sensor%20works%20because%20when%20you%20hold%20the,a%20capacitively%20coupled%20series%20circuit.
Pay particular attention to the paragraph under “Try It and See”, it explains the phenomena with the ungrounded outlet in a metal box. The example given is a metal lamp with a two prong (ungrounded) cord.
Here is the article in PDF
Capacitive Coupling.PDF (199.7 KB)
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It will pick up a magnetic wave from a CFL light bulb from more than 5 feet away.
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Interesting read! I tried the lamp example. Pretty neat. I will keep the article in mind for the next time I find an outlet that shows hot on both sides.
I looked for a license or association and didn’t see one.
Makes us TN proud 
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