Not that it's specific to Bay-to-Breakers. Just about any race I run these days uses some form of chip. I prefer the type in this post because the chip, along with the race number, are disposable and I just have to pin the number on like I would normally. The older tech was a tag that zip-tied to your shoe, and had to be turned back in at the end. Not a huge deal, but attaching a tag to my shoe so that it doesn't flop around, and doesn't cause a numb spot on my foot, is just one more thing to do pre-race.