With the help of a laser pointer and a sensitive amplifier, you can conduct an interesting experiment.Install a sound source near the glass, it can be a radio receiver, etc.If you put a laser beam at an angle on the glass, it will reflect off it.But this will already be a sound-modulated laser beam.Now it remains to take this beam with a photodiode and amplify it and listen to the sound reflected from the glass at a distance of tens and hundreds of meters.
I used the most ordinary, safe laser pointer.
An amplifier with three transistors, a photodiode is installed at the input.The resistor R3 regulates the sensitivity of the amplifier.
Install a sound source next to the glass and move away so as not to hear this sound.Aim the laser pointer beam at the glass at an angle.
Catch the beam reflected from the glass with a photodiode and listen to the sound.
