In the movie its shown that spirit can't capture Shaina's soul until she has "mangalsutra". So spirit took out the mangalsutra from car and put it in the coat. If it want to get rid of mangalsutra, it should have thrown it in garbage box or elsewhere outside the house so that Rehaan couldn't find it. Why to hide it in house?
Shaina keeps the laptop on the floor.
But when water from the table drops on laptop, its position was changed. See the position of laptop from table.