There are many Hindi films that were based on the "invisible man" concept. "Mr. X" (1938), "Mr. X" (1957), Elaan (1971), Mr X in Bombay (1964), "Mr. India" (1987), Professor Ki Padosan(1994) and "Mr. X" (2015) were some of the other Hindi films that featured an invisible protagonist. But and except Mr.India none of the film was particularly successful. In the Mr X movies and Professor ki Padosan, the hero becomes invisible using a potion or chemical.
The film under consideration is Elaan (1971) where the hero Vinod Mehra plays a journalist who is caught by the goons and imprisoned where he meets a scientist who gives him a ring that makes him invisible. The film also features Vinod Khanna in a negative role and Rekha. The film is a sci fi suspense thriller with the invisible ring used for technical effect.
In most invisibility stories, either the device-user disappears fully, along with the clothes he is wearing (Mr India, The Lord of the Rings), or the body disappears but the clothes can still be seen (the 1933 Invisible Man with Claude Rains, the Kevin Bacon-starrer Hollow Man). The science of Elaan is a little more complicated: you have to take off all your clothes if you want to turn invisible – otherwise it won’t work at all. Also as soon as a cloth is thrown at the person the person will become visible. Also the ring is not supposed to be used on finger but rather put in the mouth.
Elaan is campy fun movie with good graphics and tight editing but the film didn't work at the box office.