Comment by mesrik

That Dan Gelbart lecture where he also explains how retroreflection[0] is used to detect remote viewing, was it anything with a lens or even human eye is really good.

[0] straight link to where he explains retroflection https://youtu.be/0MtRxX0crjU?t=3019

Also many other videos where he explains how to solve hard problems are really good too.

e: There seems to be commercial product using retroreflection advertised Youtube

https://www.youtube.com/watch?v=NaXSRpTeMbU