A stall warning device must be set to operate

I presume u know the definition of Stalling speed.

Suppose 115 Knts is stalling speed of certain aircraft type.
So one wouldn't want notification of stall at same speed it has to be more than 115 Knts ie. Above stall speed, probably at speed around 120 Kts or so.., and please do correct me if i'm wrong ;)

danieldodd455, please study aerodynamics before writing comments like "bollocks".

A 'warning' device informs you of a condition that is impending. You want to be warned of a stall before it happens!

Of course! :) Not after stall.

so the right answer is: at a speed just below stalling speed?

No, correct answer is above stalling speed.

as aircraft gets faster it will obtain more lift. remember the formulae L=1/2*rho*V^2*CL. The only nature that aircraft that will jeopardise the aircraft is only structural limitation. that's why mach meter exist. Oppositely,from the formula if aircraft gets slow and slower eventually it will stall at a certain speed(lost of lift)...or if the angle of attack is beyond Critical angle of attack, it will stall too(air separation on wing). Of course in the case of speed you want the warning to kick in before the stall speed is reach which is at a higher velocity than stall speed. Don't gets confuse from Cl vs AoA graph. If based on that graph, it is at angle of attack before CLmax/stall happens.

so the right asnwer if before or after because i got confused by avionics user.