Does he ever switch it off? "No," he admits slightly sheepishly. "It is on 24 hours a day because you never know when a big story will break."
Today Mr Hart is not only by far the longest serving teachers' union leader, but - with more mentions in The TES than any other general secretary this year - he has also taken over Nigel de Gruchy's title as king of the killer quote.
But it is not just good relations with journalists that he prides himself on. NAHT colleagues speak admiringly of his dedication to members'
He joined the association as general secretary in 1978, having been a solicitor with a London law firm, Royds Barfield, where he had provided the association with legal advice.
Back then the NAHT had headquarters that you "could get into a shoe box" and debates at his early annual conferences "interminably revolved around discipline".
But since then delegated school budgets, inspections, targets and league tables have revolutionised heads' jobs and Mr Hart's role in representing them. Today, the energetic 62-year-old estimates he works a 70-hour week, dividing his time between his Cumbrian home, London, and NAHT headquarters in Haywards Heath, Sussex.
Does he enjoy such an intensive job? His face lights up. "I love it. You couldn't work a 70-hour week if you didn't, you would go under."
Besides which, it was work which led him to meet his wife, Frankie - then a local NAHT president in Cumbria - in 1992. Looking back, Mr Hart realises he could have made much more money if he had continued as a lawyer. But he has no regrets. "Money isn't everything. I wanted to be able to look after heads. As a lawyer I always wanted to look after my clients and give them all my support and I viewed the membership in the same way. I suppose I still do."