It's a kitchen timer, as you might use in a kitchen. Twisting the top half winds the mechanism to the desired time, and it ticks away until the mark reaches zero and a bell is rung. A common kitchen timer.
What sets the Louvre Timer apart is that underneath its clear plastic exterior are a series of coloured stripes that can overlap each other. They are connected to the ticking mechanism in such a way that if the bell has not yet rung, the whole timer appears green; post-ringing, the timer appears red.
The overall effect is that a multitasking cook can, at a glance and from some considerable distance, ascertain if the timer has yet rung or not.