By the beginning of the current Syrian unrest in 2011, the SyAAF was suffering the limited reconnaissance capability with her MiG-21R/25R/RB fleet almost grounded and left for high demanding recon. sorties.
That, and in addition to the requirements of daily recon. over hot spots like in Homs and Eastern Ghouta and later on in most of areas of clashes, the Syrian Army was in need for Iranians to deploy their light and long-endurance UAV's.
Referring to my records, the first UAV spotted in the Syrian sky was the Iranian made Pahpad UAV over Kafar Batna town in the Eastern Ghouta of Damascus city on 6th Feb. 2012, followed by another Pahpad spotted over Homs on 14th April 2012 (of course the use of these UAV's was earlier than these dates, but that is what I can refer to from a solid reference)
The two photos above are for an Iranian Pahpad UAV -which looks a copy from the South African Denel Dynamics Seeker UAV- spotted flying over Aqraba town to the south of Damascus on 9th May 2013.
The second type of UAV's appeared in the Syrian sky is the Iranian made Mohajer UAV which was first seen -again referring to my videos- flying over Mu'addamiyet AsSham in the Ghouta of Damascus on 13th April 2013.
The two photos above as well are for a Mohajer UAV spotted also over Aqraba town on 7th May 2013.
Mohajer UAV flying over Eastern Ghouta of Damascus on 14th May 2013.
Mohajer UAV is known with its four variants, the upgraded one 'Mohajer-4' was first seen flying over Erbeen town near Damascus on 24th Jun. 2013.
The photo above is for a Mohajer UAV spotted also over Eastern Ghouta recently.
The third type of UAV is also an Iranian made, the Yasir UAV which was first seen flying over Qalamoun mounts in Nov. 2013.
The two still above are for a Yasir UAV spotted flying over Eastern Ghouta villages on 19th Apr. 2014.
The fourth type and the newest UCAV (Unmanned Combat Aerial Vehicle) referring to its capabilities to carry weapons, is Shahed-129 which recorded its first appearance over Syria on 10th Apr. 2014 as can be seen in the photo above.
The UAV's did not fly peacefully over Syria as the rebels could bring down many of them. he first incident was happened on 22nd May. 2013 when they could shot down a Pahpad UAV was flying over Mleha of Damascus as can be seen in this VIDEO.
The photo above is for another Pahpad with serial 3-2-R0105 brought down over Eastern Ghouta on 12th Jun. 2013 as can be seen in this VIDEO.
The third and fourth Pahpad were downed over Eastern Ghouta on 2nd Oct. and 8th Oct. 2013 respectively as can be seen HERE and HERE.
The Yasir UAV was first downed somewhere in Qalamoun mounts on 7th Dec. 2013 as can be seen in this VIDEO, while the SECOND was downed on 9th Apr. 2014 also in Qalamoun area.
Away from Damascus area the first UAV was downed on 19th Dec. 2013 over Al-Ghanto town in Homs county, should be Pahpad type as can be seen HERE and HERE.
Finally, I would recommend to have a glance over Oryx's posts about YASIR and SHAHED-129 UAV's in order to know more about capabilities and development of each.