You may not have heard that recently the Las Vegas airport switched to RF Tracking of luggage. In addition to the bar code on the paper tag, inside is an RF tracker with a microchip, similar to that used to sense casino chips. It's likely this use will eventually spread to other cities. Purpose is to keep track of your bag as it travels from checkin to the plane and bag. Below is a scan of the tag for my return to Portland.

You might want to consider tearing off the tag when you pick up your bag. There is no reason that someone else could not track you with this same technology as I don't believe it is deactivated by the airline when your bag leaves the airport.