Wen,

I've never heard of the tapping or the use of a laser gun.

I do know personally that if a window is suspect of a lost thermal seal you can hold a piece of ice against the glass panel for about a minute or two and then pull the ice away and you'll droplets in between the panes of glass.

If you see the droplets, it has a lost thermal seal.

Some of the window guys use dry ice for a quicker test I've seen.

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Rick Hurst_Home Works Inspection Co_Rockwall TX
In the words of Mike Tyson.... "Everyone has a plan until they get hit inda mouf"