I keep mine in my apartment. If someone gets in to steal my bikes, they'll steal my other stuff too. As far as riding them outside, when I ride around in the city, I carry a Master Lock "Big-A** Hardened Chain" type lock with a flat key. If I'm out at the trail, I'll just lean it against a tree or something while I fill my water bottles just like everyone else does. The trail is in such a location that there are either a lot of people watching the bikes or there is nobody around for miles to steal them.