I suggest you read the directions once or twice while you wait for delivery or at least prior to even opening the box. It is not that hard once you understand them - the problem is that they are a poor Chinese translation at best. The most important part to understand is how to code the sensors. Online instructions are here: http://www.gsmalarmsystems.com/alarmmanual/gsmalarmsystemg50.pdf
NOTE: the A0-A6 that you must set on every sensor must be in reverse of what is listed on your alarm unit! The instructions are very unclear on this due them leaving out a digit in the example.
The PIR motion sensors are worthless if you have a pet. I have ordered some Pet PIR's from another site since LightintheBox doesn't carry them.
The included siren cord is not long enough. Buy an aux cable extension for $2. It is also not loud enough for larger homes. Buy a wireless siren or siren/strobe and an aux y-cable to connect both sirens.
Entire installation of 20 zones took 6 hours. 4 hours to program all sensors, 1.5 hours to understand the panel and program it and the SMS settings. A couple of minutes to mount the sensors.