How can pagers in Lebanon be infiltrated?

Hundreds of paging devices used by members of Hezbollah exploded on Tuesday across Lebanon, killing 12 people, including two children, according to the Lebanese Health Minister Firass Abiad on Wednesday.

Shortly after 1200 GMT on Tuesday, hundreds of paging communication devices began exploding across Lebanon.

Hezbollah swiftly pointed the finger of blame at Israel, though Israel has yet to issue any comment on the attack.

A source close to Hezbollah, asking not to be identified, told AFP that "the pagers that exploded concern a shipment recently imported by Hezbollah" which appear to have been "sabotaged at source".

After The New York Times reported the pagers had been ordered from Taiwanese manufacturer Gold Apollo, the company said they had been manufactured by its Hungarian partner BAC Consulting KFT.

Gold Apollo has established a "long-term partnership" with Budapest-based BAC Consulting KFT to use its trademark and the model mentioned in media reports "is produced and sold by BAC," the company said in a statement.

"This was more than lithium batteries being forced into override," said Charles Lister of the Middle East Institute.

"A small plastic explosive was almost certainly concealed alongside the battery, for remote detonation via a call or page."

Israel's spy agency "Mossad infiltrated the supply chain", he said.

A senior Lebanese security source told Reuters that the Mossad injected a board inside of the device that has explosive material that receives a code.

"It’s very hard to detect it through any means. Even with any device or scanner,”

The source said 3,000 of the pagers exploded when a coded message was sent to them, simultaneously activating the explosives.

'Lock them in an iron box'

Another security source told Reuters that up to three grams of explosives were hidden in the new pagers and had gone “undetected” by Hezbollah for months.

The attack appeared to have been many months in the making, several sources told Reuters.

In a televised speech on February 13, the group’s leader Hassan Nasrallah warned the members of the group that their phones were more dangerous than Israeli spies, saying they should break, bury or lock them in an iron box.

Instead, Hezbollah opted to distribute pagers to members across the group’s various branches – from fighters to medics working in its relief services.

Hezbollah already had concerns about the security of its communications after losing several key commanders to Israeli strikes in recent months.

Hezbollah has been using pagers as a low-tech means of communication in an attempt to evade Israeli location-tracking, two sources familiar with the group's operations told Reuters this year.

A former Israeli official told Axios that Israel had planned to use the exploding pagers as an opening blow in an all-out war with the group, but had become concerned in recent days that the booby-trapped devices could be discovered.

Al-Monitor reported that two members of Hezbollah had recently raised concerns about the pagers.

According to Axios, Defense Minister Yoav Gallant updated the US a few minutes prior to the attack that an assault was about to take place, but did not give details.