The Fifth Doctor used the Fourth’s Sonic, until it was destroyed, preferring to go “hands free”, he did not replace it. The Tenth Doctor, when their TARDISes Crashed together, remarked: “Oh, no, of course. You liked to go hands free, didn’t you? Like, ‘Hey, I’m the Doctor. I can save the universe using a kettle and some string. And look at me, I’m wearing a vegetable!'”