Well, if in a car the registration would hive details of the owner so at least that person would be traceable. There is very little not known about us nowadays. Your name will be on a massive amount of databases eg car insurance, NHS, energy suppliers, council tax, credit companies, DWP, don't think you should worry about not being traceable. If you are unconscious, unable to communicate, the police will investigate using all resources as well as entering your home to try to get details if all else fails. Living alone is a different ballgame and unless you have some kind of system whereby your absence is noticed you may well be left until the neighbours notice!! Very unlikely of course unless you are a hermit. Always have contact details in your home.