In June 2013, Snowden revealed the NSA was collecting the phone records of millions of Verizon customers in the US using a secret court order, and had also tapped the phones of dozens of world leaders, including Germany's Chancellor Angela Merkel.
Snowden was threatened with prosecution in the US, and fled to Russia, where he was granted asylum two years later.
The following year he gave an interview in which he explained how the NSA, and Britain's GCHQ, had the capability to use smartphones like bugs in a room.
They were able to switch on people's phones and listen to them remotely without them being aware, he said.
"They can absolutely turn them on with the power turned off to the device," Snowden said.
He said the intelligence agencies could gain access to a handset by sending it an encrypted text message and could even use the phone's camera without the owner's knowledge.
The Washington Post had reported the NSA had introduced this feature to help US forces hunting al-Qaeda insurgents in Iraq.
Earlier this year, WikiLeaks exposed a CIA program aimed at hacking computers, mobile phones and even smart TVs from companies like Apple, Google, Microsoft and Samsung, using techniques users could neither detect nor disable by resetting their devices.
After Snowden's little revelation some people who were extremely concerned about government surveillance — including criminals and terrorists — began removing the batteries entirely from their devices.
The world now see that your act was heroic and you helped to transform an entire generation that — thanks to you — knows what privacy means. pic.twitter.com/NVmADhV8UR— David Miranda (@davidmirandario) 14 July 2017
Now a number of smartphones, like the Samsung A5, have come on the market in the UK, US and elsewhere, which have batteries which cannot be removed.
Some conspiracy theorists might jump to the conclusion that they have been pressured by the intelligence agencies to ensure smartphones can always be spied on.
"Seemingly the main reason is waterproofing, but they have already achieved that with a removable battery in the S5," Tonny Be, a technology expert, told Sputnik.
"The heads of Google and several other phone/tech manufacturers have been documented in the media as having visited the White House during the Obama era," he told Sputnik.
"Advancement of non-removable batteries started to invade the mobile market… coincidence or plan to keep everyone on the grid while milking money out of them with neutered devices while keeping those same devices 'always on' to be spied upon by the powers that be?" Mr. Be said.
"You decide: conspiracy theory lunacy or nice, complete, neatly-wrapped package of evidence being touted as coincidence?" he added.
"I figure if the powers that be ever admit to it being a collective effort that was forced upon manufacturers or possibly agreed upon to be tactically put in play, they'll spin it in as a preventive terrorist measure," Mr. Be concluded.