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

At the time of publishing, at least nine people have been killed and 2,750 wounded, according to security services and the Lebanese health minister.

Pagers are small communication devices used commonly before mobile phones became widespread.

The devices display a short text message for the user, relayed by telephone through a central operator.

Unlike mobile phones, pagers work on radio waves, the operator sending a message by radio frequency – rather than the internet – unique to the recipient’s device.

It is thought that the basic technology used in pagers as well as their reliance upon physical hardware means they are harder to monitor, making them popular with groups such as Hezbollah where both mobility and security are paramount.

What happened?

The series of explosions began at about 4:45pm and lasted for around an hour.

Casualty numbers are still being confirmed.

One eight-year-old girl has been confirmed among the dead.

Mohammad Mahdi Ammar, the son of Hezbollah MP Ali Ammar,  has also been reported killed.

Hezbollah confirmed that two of its fighters had been killed.

Lebanese Health Minister Firass Abiad told Al Jazeera: “About 2,750 people were injured, … more than 200 of them critically” with injuries mostly reported to the face, hands and stomach.

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

Who carried out the attack?

Many people, including Hezbollah, are pointing to Israel.

Israel and Hezbollah have been engaged in a mostly low-level exchange of fire over the Lebanon-Israel border since October 8, the day after Hamas-led attacks on Israel killed 1,139 people, saw about 240 taken captive and set off Israel’s war on Gaza.

Recently, Israeli politicians and media have increasingly talked of military action against Lebanon to drive Hezbollah back from the border to allow for the return of about 60,000 Israelis evacuated right 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 from Lebanese Information Minister Ziad Makary, Israel itself – in keeping with previous situations – remains tight-lipped.

Why didn’t similar blasts occur in Gaza?

According to Hamza Attar from the Department of Defence at King’s College in London, “They cannot use the same method in Gaza because Hamas is very cyber-aware compared to Hezbollah.

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

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

We still don’t know.

Some speculation has focused on the radio network that pagers rely on, suggesting that it may have been hacked, causing the system to emit a signal that triggered a response within the already doctored pagers.

“What I think happened [is that] every Hezbollah [member] who was at a specific level was attacked,” data analyst Ralph Baydoun told Al Jazeera.

He also suggested that Israel would not need to know the names of whoever received the corrupted signal but it could gather valuable intelligence after the detonations.

“If they had the satellites on, … they would know the names and locations of all operatives who were attacked … immediately when [they asked] for help. They would disclose [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 tampered with along the supply chain and “wired to explode on command”.

If the pager’s lithium battery was triggered to overheat, this would kick-start a process called thermal runaway.

Essentially,  a chemical chain reaction would occur, leading to an increase in temperature and eventually the battery’s violent explosion.

However, triggering that chain reaction within multiple devices that have never been connected to the internet is far from straightforward.

“You have to have a bug in the pager itself [so that] it will overheat as a result of certain circumstances,” Baydoun said, speculating that those circumstances would most likely be a trigger introduced into the pager through doctored code.