Israel’s 40-mile-long chain of walls and fences at its Gaza border teems with sensors and automated weapons. It is supported by an electronic intelligence network that monitors every phone call, text message and email in the territory. A large, well-trained military stands ready with state-of-the-art weaponry to respond rapidly to threats.

These defenses were built upon much the same technology that the U.S. military uses to keep its citizens safe and watch over its interests around the world and NATO armies use to monitor the border with Russia and the Middle East. So when thousands of Hamas militants slipped through Israel’s defenses on October 7, killing 1,200 Israelis and taking about 240 hostages, what presumed to be a vast technological advantage suddenly seemed deeply flawed.

The attack left Israelis, both citizens and military experts, deeply shocked at the country’s vulnerability. It has also reverberated through the halls of the Pentagon and the military establishments in many countries. Military experts are worrying about what some see as an overreliance on high-tech security to keep installations and homelands safe from attack. If Israeli security can’t protect against a relatively low-tech terrorist organization like Hamas, what havoc could Russia, China or some other advanced adversary deliver?

“The lessons for the Pentagon are huge,” says Amy Nelson, a foreign policy fellow at the Brookings Institution. “The countries with the highest tech defenses and the most modern militaries won’t necessarily win the battle. Surprise attacks can still get through.”