The Prime Minister says he won't take a cellphone into confidential meetings and throws his handset away every three months for fear of being spied on.

John Key. Source: 1 NEWS

Asked about whether he was worried about his phone conversations being recorded, John Key told More FM he was cautious about what was said on phones.

"I have more security than most people would have. But it doesn't mean you can't break into it," he said.

"If I was having a conversation with my national security advisers ... I would never have a mobile phone in the room I'm in, because you can use it as a listening device."

He said he regularly changed handsets, usually throwing them out after three months.