I can remember seeing a sci-fi film on TV (from 1960's) over here in the UK. Aliens could only been seen through glasses and a man gave a woman a pill to calm her down before she put them on.
I can't find the name of the film though.
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Is it "The Love War" from 1970?
It's about warring aliens on earth and they can see each other only by using special glasses.
Two warring planets choose to settle their conflict over which of them will take over the planet Earth; by each sending a trio of soldiers to the Earth, to do personal combat to the death. The loser's planet cedes the conquest of the earth to the winner of the combat. The combatants, disguised as human beings, can only identify each other by using special visors.
One name that comes to mind is They Live from the year 1988.
I remember that he could also see subliminal messages (in black and white) in all the advertising and some other things as well, but I cannot remember the tablet event which you mentioned. I cannot recall a similar movie from the 60's, but this may have been a remake of the same.