The one barely visible in the following video is a drone flying over Homs, Syria.
Although, at first glance, its color, shape, etc. reminded me those of the U.S. Global Hawk, believed to be operating over Syria, its sound is the one of a propeller-driven engine. Unless some Israeli Herons, or U.S. Predators or Reapers are already operating well inside the Syrian airspace, this could be another (unidentified) drone belonging to the Assad forces.
Footage in this case is extremely low on quality and, unlike the “Pahpad” spying on the clashes, identification in this case is almost impossible. It could be another “Pahpad” or a “Mohajer 4” even if it seems to be white/light grey in color, sensibly bigger and it is flying higher (although this could be a distortion of the camera) than the ‘bots spotted so far.
Even if what was flying in the smoke in a previous video still remains a mystery (I suggest you reading all the comments to the post to find some interesting theories) someone has explained that smoke is intentionally created to prevent UAV (Unmanned Aerial Vehicles) from targeting activities on the ground.
Thanks to Bjørn Holst Jespersen for the heads-up.