Hundreds of pagers belonging to the Lebanese armed group Hezbollah have exploded simultaneously across Lebanon.

At the time of publication, at least nine people have been killed and 2,750 injured, according to security services and the Lebanese Health Minister.

Pagers are small communication devices that were widely used before cell phones became widespread.

The devices display a short text message to the user, which is relayed via the phone to a central operator.

Unlike mobile phones, pagers operate using radio waves. The operator sends a message via a radio frequency (rather than the Internet) that is specific to the recipient’s device.

It is believed that the basic technology used in pagers and their reliance on physical hardware makes them more difficult to control, making them popular with groups such as Hezbollah, where both mobility and security are paramount.

What happened?

The series of explosions began around 4:45 p.m. and lasted about an hour.

The number of victims is still being determined.

An eight-year-old girl is said to be among the dead.

Mohammad Mahdi Ammar, the son of Hezbollah MP Ali Ammar, was also reportedly killed.

Hezbollah confirmed that two of its fighters were killed.

Lebanese Health Minister Firass Abiad told Al Jazeera: “About 2,750 people were injured, … more than 200 of them are in serious condition,” with injuries reported mainly to the face, hands and abdomen.

Iran’s ambassador to Lebanon, Mojtaba Amani, was also injured in the explosions.

Who carried out the attack?

Many people, including Hezbollah, point to Israel.

Israel and Hezbollah have been engaged in a predominantly low-level firefight above the Lebanon-Israel border since October 8, a day after Hamas killed 1,139 people in attacks on Israel, captured some 240 and launched Israel’s war on Gaza.

Recently, Israeli politicians and media have increasingly talked about military action against Lebanon to drive Hezbollah from the border and thus allow the return of some 60,000 Israelis who were evacuated shortly after the attacks began.

“We hold the Israeli enemy fully responsible for this criminal aggression,” Hezbollah said in a statement, adding that Israel “will certainly receive its just punishment for this sinful aggression.”

Despite a similar condemnation by Lebanese Information Minister Ziad Makary, Israel itself – as in previous situations – remains tight-lipped.

Why didn’t similar explosions occur in Gaza?

According to Hamza Attar of the Ministry of Defence at King’s College London, ‘they cannot use the same method in Gaza because Hamas is much more aware of cyber attacks than Hezbollah.

“They are very capable when it comes to telecommunications,” he said of Hamas, emphasizing the group’s efforts to encrypt communications.

“They don’t use phones or cell phones. They have their own network and internet and communications and don’t need anything above ground,” he said.

We still don’t know that.

There is speculation about the radio network that pagers rely on. It is suggested that this has been hacked, causing the system to send out a signal that triggers a response within the already compromised pagers.

“What I think has happened is that every Hezbollah member who was operating at some level has been targeted,” data analyst Ralph Baydoun told Al Jazeera.

He also said that Israel did not need to know the names of those who received the manipulated signal, but that it could gather valuable information after the explosions.

“If they had the satellites on, … they would know the names and locations of all the agents that were attacked … immediately when (they) called for help. They would give (their) locations,” he speculated.

Other analysts, such as former British army officer and chemical weapons expert Hamish de Bretton-Gordon, suggested that Hezbollah’s pagers may have been manipulated throughout the supply chain and “enabled to detonate on command.”

If the pager’s lithium battery were to overheat, it would initiate a process called thermal runaway.

In fact, a chemical chain reaction would take place, leading to a temperature increase and ultimately a violent explosion of the battery.

However, it is not that easy to start such a chain reaction across multiple devices that have never been connected to the Internet.

“There has to be a bug in the pager itself that causes it to overheat due to certain conditions,” said Baydoun, who speculated that those conditions would most likely be a trigger introduced into the pager via manipulated code.