Conerting monitor's normal screen into touch screen

I jusy came across the topic in formu discussion at URL :

I then googled the matter and came up with answers the finds and one or 2 web sites are as under

(i) Search result - Google

(ii)Commercial way to DIY (do it yourself)at some cost.

(iii) By attaching some devices etc - this is what the member who posted at url in the beginning was needing I think.