If your source code is really that important (if, say, it’s a trading strategy, or will run a nuclear submarine), then you insist that people work five days a week from the office, using desktops (not laptops), make them drop off personal devices as they enter the office, and give them extra time off for doctors appointments, train strikes, etc. I once interviewed at a place that did this, as a competitor had previously tried to steal their code.

Otherwise, don’t worry about it.