There is a passcode that is really tough to replicate- behaviour - aka habbits. Every day, you travell down the same road, meet the same people (okay as your cellphone the same cellphones, wifi-stations). This habbit is like a fingerprint, as in, there are very few people who have the exact same browsing behaviour. If you could extract a fingerprint from that information, you have a sort of biometric identifier that is at least hard to come bye.

Problem- every holiday your phone thinks youre a phonethief