It's caused by multiple factors (some of them are based on Israel's technological advantage) - shelters are everywhere, Israelis are trained really well (even falling to the ground before a rocket impact reduces casualties), they have sophisticated warning system - they even have an app for that [1]

Obviously I cannot tell how efficient Iron Dome is but they certainly have other effective tools at their disposal.

[1] http://www.computerworld.com/s/article/9249866/Red_Alert_app...