Below the sticker we have two Philips screws (red). Unscrew them.

Edit according to Simon (see comment): In the yellow slot there is a tab that is to be pushed down to unlatch it. If you insert a pick in the seam between the top and the bottom half of the device it should open easily when downward pressure is applied to the latch..

Now carefully pry apart the two halves of the cover, starting from the side of the battery compartment.