How could pagers in Lebanon have been rigged to explode?

At least nine people were killed and nearly 3,000 people wounded across Lebanon on Tuesday afternoon when hundreds of pagers used by Hezbollah and others almost simultaneously exploded.

Hezbollah has blamed Israel, where officials and the military have made no comment.

Many modern pagers use lithium-ion batteries — similar to the ones found in smartphones — which are capable of exploding.

However, battery experts say that it’s very unlikely the pagers could have been triggered to explode with only a wireless signal — and that the descriptions and video of the attack is inconsistent with battery explosions.

We talked with experts to answer some basic questions about how the attack could have been carried out.

First, why is Hezbollah using pagers?

Hezbollah switched from cellphones to pagers in recent months in an attempt to avoid tracking and surveillance.

Phones constantly send signals to nearby cell towers to register their location, enabling calls to be properly routed. Eavesdroppers can intercept these pings to determine their location.

Experts said it’s difficult to discern the exact security benefits the pagers provide without knowing the specific models. Many pagers only listen for incoming signals and do not send them. This makes tracking harder.

In addition, some pagers lack the GPS technology that is nearly universal in modern cellphones.

Popular in the 1980s and 1990s, pagers are still used in some physical high-stakes jobs that require reliable extended communication due to their longer battery lives.

In the United States, users include personnel in the medical field — such as doctors and emergency medical technicians — and some nuclear power plant operators.

Could a cyberattack trigger off-the-shelf pagers to explode?

Lithium-ion batteries can explode if they’re short-circuited. When this happens, the battery releases gas and heats up — potentially to well over a thousand degrees. This process is called thermal runaway. When the gas reaches a certain pressure in the battery, it explodes.

Some Hezbollah members reportedly felt their pagers heat up before they exploded.

But given the strength of the explosions and how consistent and coordinated they were across thousands of devices, electrical engineering and battery experts said the attack likely required modifying the pagers.

Battery experts said it’s unlikely that a wireless signal alone — with no physical alterations — could cause thermal runaway, which typically occurs when a battery overheats, sustains physical damage or overcharges.

It’s possible to remotely deactivate the software that coordinates a safe charging. But because the exploding pagers were worn by Hezbollah members, and not being charged, this mode of failure is unlikely.

To trigger an overheating failure, the pagers would have to reach at least 140 degrees, said Scott Moura, an engineering professor at UC Berkeley who studies battery safety. But modern consumer electronics are designed to prevent overheating, so there would likely be no simple software that could achieve these temperatures.

To achieve a battery explosion, Moura said, “I think it would be much easier to physically modify it.”

When batteries do explode, does it look anything like what happened in Lebanon?

Most of the injuries in Lebanon were to the face, hands or stomach — near where the pager would be carried.

“I’ve been involved in law cases where batteries have been in pockets and burned their legs or where vaping products have done severe damage to the face,” said Michael Pecht, an engineering professor at the University of Maryland who studies battery reliability.

But he and other experts said the fatalities suggest that these explosions were different.

“When these things fail, they can burn people and do some damage,” said Ofodike Ezekoye, a University of Texas at Austin professor who studies how lithium-ion batteries can fail. “But it’s very rare for one of these to be able to kill someone.”

How could the pagers been physically modified to explode?

Causing a short circuit in a battery to trigger thermal runaway and an explosion with a physical alteration is fairly straight-forward, Pecht said. The batteries can even be modified to explode at a reliable time after the short circuit is triggered.

However, he and other experts said, creating an explosion consistent with the footage would probably require more extreme modifications.

Perpetrators could’ve added an explosive chemical to the battery cells that would be hard to detect, Ezekoye said. Then, with a small electric signal, trigger them to explode.

He said confirming the true mechanism would require studying the pagers in question. “I would imagine the Lebanon authorities are trying to find any possible pagers that did not fail,” he said.

Have similar attacks been carried out before?

Exploding consumer electronics is not a new tactic.

In 2010, Al Qaeda planted explosives inside two printer cartridges on UPS and FedEx cargo flights. In 2016, a bomb inside a laptop exploded during a Somali passenger flight, injuring two people.

Israel is suspected of using an exploding phone in 1996 to target a Palestinian bomb-maker. In that case, the phone was physically modified and the operation did not involve malicious software.

Still, exploding electronics have never been used on the scale seen Tuesday in Lebanon.