Among IDF's measures to reduce civilian casualties were the extensive use of leaflets and phone messages to warn Palestinians, including families in high-risk areas and families of Hamas personnel, to leave the area or to avoid potential targets. Israel used F-4 Phantoms to deliver more than 2 million leaflets urging the population to evacuate. In a practice codenamed roof knocking, the IDF issued warning calls before air strikes on civilian buildings. Typically, Israeli intelligence officers and Shin Bet security servicemen contacted residents of a building in which they suspected storage of military assets and told them that they had 10–15 minutes to flee the attack. At several instances, the IDF has also used a sound bomb to warn civilians before striking homes. In some cases, IDF commanders called off airstrikes, when residents of suspected houses have been able to gather on its roof. IAF developed small bomb that is designed not to explode as it was aimed at empty areas of the roofs to frighten residents into leaving the building. Israel's military used low-explosive missiles to warn civilians of imminent attack and to verify that buildings were evacuated before attacks. Some of the attacks took place sooner than the warning suggested and many calls were not followed up with attacks. The Israeli Government report notes that while the warning systems implemented by the IDF did not eliminate all harm to civilians, they were apparently effective, because in many incidents aerial video surveillance by IDF forces confirmed the departure of numerous residents from targeted areas as a direct result of the warnings before the attacks.
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from the article: IDF chief: Gaza war against Hamas was an 'excellent' operation