Brush is an iOS app that turns any supported iOS device into a broadcasting and monitoring wireless beacon, using the Bluetooth 4.0 Low-Energy protocol. While the bluetooth radio is on, the device looks for other Brush beacons nearby. If there is a signal within range, the app's UI will indicate approximate distance. When the devices "brush" by coming within a few feet of each other, the information is pushed to a NodeJS server backed by a Mongo database containing the time, location, and users involved. Finally, the server pushes changes in real time to the Brush website, using WebSockets and a live-updating SVG graph representing encounters between users.