[Narvin's pessimistic enough to read between the lines. And he's already decided that if it looks like he'll be captured, he'll simply kill himself. Better to get it over with quickly and death toll safely on the Barge than to die slowly in an arena or a laboratory.]

There's a series of advanced locks on the cabin door. The TARDIS itself is also locked and if an unauthorized person breaks in the life support system will immediate emit a gas to render the intruder unconscious. If the TARDIS still detects motion three seconds later, the whole interior is electrified, every door and hatch is locked down, and all systems shut off and can't be reactivated without my unique artron signature and Rassilon imprimatur.

[Narvin is a bit paranoid about someone trying to steal his TARDIS.]