The port city of Ashdod, 24 km north of the Gaza border, was this week connected to the rocket alert system already in use in Ashkelon and Sderot. It is an acknowledgement that threats by Palestinian militants to bring it within range are being taken seriously.
The move comes as an escalation of fighting continued to shake the five- month-old ceasefire between Israel and Hamas along the Gaza border.
Although Israel lifted its closure on the coastal enclave to allow supplies in on Monday, army officials said the virtual blockade maintained since November 4 would continue because of ongoing Palestinian rocket fire. Around 150 missiles have been fired since that day and more than 20 since Sunday, the officials said. Twelve Palestinian militants have been killed and one Israeli woman was slightly wounded by shrapnel in Sderot.
Eddy Ben-Hamo, the Ashdod municipality spokesman, said after a visit to the city by deputy defence minister Matan Vilnai, that the installation of the Colour Red early warning system was totally routine and was "part of an existing plan. We always prepare for what is coming".
In Gaza City, business consultant Sami Abdul-Shafi said the 1.5 million residents were feeling the pinch.
"We are not facing famine or hunger but that is not the only criteria for gauging the health of the Gaza Strip," he said.
"We are facing scarcity of fuel and all the necessities of life." He warned that the shortages were not making Hamas less popular.
"As a resident of Gaza I criticise Hamas when it makes mistakes, but I can't blame Hamas for what is happening due to the tightening siege."
Israel rebuffed international criticism, including from the UN High Commissioner on Human Rights, Navi Pillay, who said the closure was illegal and caused "massive human suffering".
The Israeli foreign ministry responded that the commissioner had fallen victim to "Hamas's cynical manipulation of the media" and that Hamas bore responsibility for the situation. Israel would be ready to allow supply trucks in again "as soon as Hamas ends its violent attacks".