If you’re boarding a plane, chances are you’ll be bringing a phone aboard with you. But the technological sophistications of phones have left airlines and governments with safety concerns — and in the case of Samsung’s new faulty phones, the concern is very real.

On Saturday, the US Department of Transportation officially banned Samsung’s Galaxy Note 7 smartphones from all aeroplanes in the United States. “Passengers who attempt to evade the ban by packing their phone in checked luggage are increasing the risk of a catastrophic incident,” the department’s new guidelines state.

The news stories are well known, at this point: A few weeks after the Korean electronics giant launched the phone in August, reports from around the world of the lithium batteries catching fire during or after charging started flooding in. Around 2.5 million phones were sold globally, until Samsung finally announced a worldwide recall. Earlier this month, the company then announced it would permanently cease production of the phone once and for all.

This is yet another case of how phones have posed headaches for airline companies and government organisations over the years. While electronics spontaneously bursting into flames pose a clear danger, other issues are less clear leaving most of us still unsure of what is deemed safe or unsafe.

Phones as terrorist weapons

In a post-9/11 world, the fight against terrorism, combined with the meteoric rise of the personal electronic devices (PEDs), has left the relationship between planes and mobile phones extremely complicated.

In 2014, the US Transportation Security Administration, the government agency established in 2001 in response to the September 11 terrorist attacks, introduced a new rule for bringing PEDs on flights: If travelling from another country to the US, your devices must have enough battery charge in them to turn them on upon request by a security agent.

The reason? A concern that global terrorists could replace batteries in portable electronics like mobile phones with tiny bombs. These bombs could potentially go unseen or undetected, even with X-rays or metal detectors, the agency said. It’s part of “enhanced security measures” that apply to certain airports, including direct flights between the US and the UK.

How real is this threat, though?

It was real enough for the TSA procedures to come at the behest of the US Department of Homeland Security. “Aviation security includes a number of measures, both seen and unseen, informed by an evolving environment,” Secretary of Homeland Security Jeh Johnson said in a statement in 2014, without providing much more context or explanation. The TSAstarted suggesting that travellers keep chargers handy at airport gates.

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