In Cory Doctorow's book Little Brother, the protagonist defeats gait sensors with some pebbles in his shoe. It's really not such a bad idea, as every step is going to be different as your foot tries not to hit the pebble too hard.

Do you have a database of walking styles? Does anybody?

They definitely have access to most people's photos - driver's licenses, passports.

I personally don't care if they know where I go in public. They can just tail me if they really want to know.

> Do you have a database of walking styles? Does anybody?

I nearly always walk around with a 3-d accelerometer which can indeed "phone" home.

Here's the ML extraction mechanism as explained by a Samsung engineer - http://www.slideshare.net/satnam74/the-fifth-elephant-2013-t...

Yeah but if they have access to your phone, they already know where you are, no need for the overcomplicated accelerometer method.

If it's in a database, then people without access to your phone can still identify you.