If you want to know how to rip them off you're in the wrong forum. On the other hand, if you want to know about coin mechs and how they work then I would suggest you phrase your question differently. As for detecting coins - it is both mechanical and electronic normally. They might do things differently in Mumbai.

This forum is normally frequented by people that have more cerebral things to do rather than ripping off phone boxes, pirating CD's or terrorist activities.