This story was produced by our colleagues at the BBC. 

In April, a massive power cut brought Spain and Portugal to a standstill, affecting millions of people.

Journalist Ashish Sharma was in Madrid, where he noticed some restaurants still serving.

“There were groups of people having meals with a nice bottle of wine and ordering a lot of stuff. I thought, ‘I hope these people have got cash on them, because they're not going to be able to use the normal machines to make payment,’” he said.

Recent cyberattacks and power outages have highlighted the vulnerability of modern payment systems, where tapping and swiping predominate. Cash offers a backup, but it’s becoming scarcer. Now, a number of countries are now bringing in laws to protect its use.

According to the Bank of Spain, the national payments system was working during the crisis, supported by servers with their own power supply. But many shops could not take card payments because their devices were out of power. (Cash was an option as long as it was already in your wallet, because ATMs were not usable.)

In Spain, there’s more cash in circulation than in many other European countries. It’s used in around 60% of in-store transactions compared to around 16% in the United States. In terms of cashless societies, Scandinavian countries lead the way, but there are now worries about how the system will function in an emergency.

In Norway, nearly all transactions are digital, but a new law means retailers can be fined if they refuse to accept cash. Carl Johannessen owns the Bergen Coffee Roastery in Bergen, Norway.

“Until COVID, we had cash, but it was a hassle because the banks didn't want to take our cash, so we needed a company to come up our cash, and then deposit for us,” he said. “But it was a lot of work and also created a lot of mistakes. After COVID, it felt so nice not to have cash.”

But the new law means cash has returned, although there's less of it. It comprises about 3% to 5% of sales at the coffee shop, so it's easier to manage.

“It's not a big deal to implement, but the baristas, when they close, have to count the money, put it in a safe, and now we deposit it once a month in the bank,” Johannessen said.

In neighboring Sweden, the central bank warned citizens to keep cash ready to use in case of emergencies. In fact, Sweden has been running an inquiry into the use of cash, proposing an obligation on shops to accept cash for essential goods.

Central bank governor Erik Thedéen thinks cash is crucial to national security.

“The reason why we have pushed for this is that it's very much a resilience issue. Of course, we have been in close contact with Ukraine, and I think also the Spanish experience now — to have something, together with credit cards … to basically have a resilient system so if one of them breaks, you can use the other one,” he said.

Natasha de Teran is co-author of “The Pay Off: How Changing the Way We Pay Changes Everything.” She's not convinced that new rules around cash will provide enough of a safety net in societies where digital systems are so entrenched.

“Are there enough staff to count the cash? Are there enough places to keep the cash safe? Can the shop bank it?” she said. “So I don't think when a society's gone completely electronic, you can come back to cash and say 'We'll be fine with cash', because I don't know that we will.”

So what about resilience for those countries that are almost cashless? “I think we need a very good grid,” de Teran said.

It's not just about cash, she added, when so much of our lives — from public transportation to communication — relies on electricity.