Israeli military forces use a "knock on roof" warning system in Gaza, to alert some residents when an airstrike is imminent.
Footage posted on YouTube by the Gaza-based Watania news agency apparently shows the controversial technique in action, with a small missile hitting the roof of what appears to be a residential building in the region. This is a "roof knock" warning.
Just over one minute later a rocket strike is blasted into the entire building, which the agency said was home to a man called Samir Nofal and his family.
In this instance the Israeli military had also provided a 15-minute phone warning ahead of the strikes and the Nofal family were able to warn neighbours and evacuate the building safely before the rockets hit.