Covering Israel with an "Iron Dome"

(CBS News) TEL AVIV - For the fourth straight day, Hamas fired missiles into Israel -- but not all of them got through, thanks to an Israeli missile defense system known as the "Iron Dome."

The sirens went off Sunday just after darkness fell. The Iron Dome interceptor system had picked up an incoming rocket.

It was the third time since it was installed Saturday, the battery scored a perfect hit.

Watch: Israel's "Iron Dome" intercepts rockets from Hamas
Medics: Israeli air strike kills 11 civilians in Gaza
Hamas links truce to end of Gaza border blockade
Obama: Israel has "right to defend itself"

The number of rockets fired from Gaza has dropped significantly, but some of them have a longer range.

The Israelis believe they were supplied by Iran -- a charge Iran has denied.

And locally-made rockets continue to get through to urban areas in the south.

Hamas says it won't quit firing until the Israelis stop bombing, end targeted assassinations and lift the economic blockade on Gaza.

The Israelis insist any long-term peace agreement must be based on no missiles from Gaza -- ever.

Based on bitter experience, neither side is willing to take the other's word, even if a deal is worked out. Therefore, Israelis are pushing ahead with plans to cover the entire country with the Iron Dome system.

Technically, Iron Dome is a defensive weapon, but it also gives the Israelis leeway to go on the offense because it greatly reduces the price they will have to pay for Hamas retaliation.

So on the ground, Israeli forces are poised waiting for their government to find a reason to invade Gaza or not.

On Sunday, Israeli Prime Minister Benjamin Netanyahu held to the hard line.

"We are exacting a heavy price from Hamas," Netanyahu said in Hebrew, adding that the Israeli military was "prepared for a significant expansion of its operations."

Israeli analysts predict a deal of some sort will be struck within 48 hours. A safer bet is that there will be more sirens to be heard.