best surveillance - listening devices?
 

Like Bionic Ear. Parabolic Microphones? Laser Microphones?

Just 50 feet away with glass window. What work best?

Need to hear conversation in room. No need to identify voice. So laser microphone on commercial markets work good yet?

I likes this but look expensive.

SPECTRA Laser M type professional laser microphone | Lasermicrophone.com

Listening devices - SuperEar - Parabolic - Shotgun Microphone -

this site has some professional equipment, jammers too.

Are you considering going into the spy or detective business? Have you any qualifications. Like any business, it's no just easy money for little work :2 cents: