I leave my bike in the basement at work. Not locked. There's usually anywhere from 15 to 25 other bikes, of which mine is kind of middle-of-the-road for value, and the building is secure (sorta...the bike room is open to the office, but the outside door near the bike room requires a keyfob from the outside...the front door is unlocked, but you have to navigate a reception area and a maze of cubicals to get to the bike room from there.) Our office headcount is 155, and any one of them could potentially steal my bike, but seriously, what would they do with it that would be worth risking their job. That said, my office is a pretty high-income environment, so the job is worth a fair bit.