An Obama aide called the move it "standard operating procedure," but veterans of a range of other campaigns said they'd never heard of the practice, which is common in secure White House spaces where there are concerns of espionage, but unknown in contexts in which only political secrets are discussed. The new prevalence of sophisticated audio and recording capacities in mobile devices owned by virtually anyone wealthy enough to write a check to a political campaign, however, has put a new pressure on campaigns concerned with staying on a public message.

The fundraising sessions are one of the last vestige of privacy for the president outside of the White House, and a rare opportunity for top donors to hear relatively unscripted remarks by the most powerful man in the world, and to ask him questions. Obama's prepared remarks at the events are open press and covered by a small group of reporters, but the "press pool" is escorted out of the room before the Q&A period.

At Romney fundraisers, attendees are greeted to signs of "Please, no audio or video recording," and like Obama events, larger fundraisers are open to reporters; a Romney spokesperson, however, told BuzzFeed that their campaign allows donors to keep their phones during fundraisers.

Former aides to presidential candidates Hillary Clinton, Rick Perry, and Jon Huntsman all expressed surprise at the practice, and they've never seen an instance where a campaign asked donors to surrender their cell phones.

The former Clinton aide called the Obama policy "absurd," suggesting that the Obama policy is almost certainly a response to the infamous 2008 fundraiser where Obama described voters in rural Pennsylvania as "bitter."