At least nine people were killed and nearly 3,000 injured across Lebanon on Tuesday afternoon when hundreds of pagers used by Hezbollah and others exploded almost simultaneously.
Hezbollah has blamed Israel, where neither officials nor the military have commented.
Many modern pagers use lithium-ion batteries (similar to those found in smartphones) that can explode.
However, battery experts say it is highly unlikely that the pagers could have been triggered to explode with just a wireless signal, and that descriptions and video of the attack are inconsistent with battery explosions.
We spoke to experts to answer some basic questions about how the attack might have been carried out.
In recent months, Hezbollah has switched from cellphones to pagers in an attempt to avoid tracking and surveillance.
Phones constantly send signals to nearby cell towers to record their location, allowing calls to be routed correctly. Spies can intercept these pings to determine their location.
Experts say it's difficult to discern the exact security benefits that pagers offer without knowing the specific models. Many pagers only listen for incoming signals and don't send them out, making tracking difficult.
Additionally, some pagers lack the GPS technology that is almost universal in modern cell phones.
Pagers, popular in the 1980s and 1990s, are still used in some high-risk physical jobs that require extended, reliable communication due to their longer-lasting batteries.
In the United States, users include medical personnel (such as doctors and emergency medical technicians) and some nuclear power plant operators.
Lithium-ion batteries can explode if short-circuited. When this happens, the battery releases gas and heats up, possibly to 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 force 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 is unlikely that a wireless signal alone, without physical disturbances, could cause thermal runaway, which typically occurs when a battery overheats, suffers physical damage or is overcharged.
It is possible to remotely disable the software that coordinates a safe payload, but since the explosive pagers were used by Hezbollah members and were not loaded, this failure mode is unlikely.
For an overheating failure to occur, the pagers would have to reach at least 140 degrees, said Scott Moura, an engineering professor at the University of California, Berkeley, who studies battery safety. But modern consumer electronics are designed to avoid overheating, so there probably wouldn't be simple software that could reach those temperatures.
To achieve a battery explosion, Moura said, “I think it would be much easier to physically modify it.”
When batteries explode, is it anything like what happened in Lebanon?
Most of the injuries in Lebanon were to the face, hands or stomach, near where the pager was carried.
“I've been involved in legal cases where batteries were in people's pockets and burned their legs or where vaping products caused serious facial damage,” said Michael Pecht, an engineering professor at the University of Maryland who studies battery reliability.
But he and other experts said the deaths suggest these explosions were different.
“When these devices fail, they can burn people and cause injuries,” said Ofodike Ezekoye, a professor at the University of Texas at Austin who studies how lithium-ion batteries can fail. “But it’s very rare that one of these can kill someone.”
Pecht said that short-circuiting a battery to cause thermal runaway and explosion through physical alteration is fairly easy. Batteries can even be modified to explode at a reliable time after the short circuit occurs.
However, he and other experts said that creating an explosion consistent with the images would likely require more extreme modifications.
The attackers could have added an explosive chemical to the battery cells that would be difficult to detect, Ezekoye said. Then, with a small electrical signal, they would have detonated them.
He said that to confirm the true mechanism, it would be necessary to study the pagers in question. “I imagine that the Lebanese authorities are trying to find any pagers that have not failed,” he said.
Have similar attacks been committed before?
The explosion of consumer electronics is not a new tactic.
In 2010, al-Qaeda placed 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 explosive phone in 1996 to attack a Palestinian bomb-maker. In that case, the phone was physically modified and the operation did not involve malicious software.
However, electronic explosive devices had never been used on the scale seen in Lebanon on Tuesday.
