So you are worried about your phone dropping out of your pocket by accident? C-Safe for smartphones can help. It physically locks your phone to your pocket, so no one else can take it out easily. C-Safe has two parts: a thin link attached to your phone and a lock clamped to the fabric of your pocket.
While this lock makes it hard for strangers to steal your phone, it lets you unlock your phone with a push and at a custom angle set by you. You can pre-order yours on Kickstarter.