This is a Bluetooth Low Energy device that attaches to a yard sign and pushes listing information to a cell phone with the RealtyBeacon app (just iPhone for now, but Android is in development).
This is a great replacement for brochure boxes and flyers, and is affordably priced. The technology is brand new, and will be developing rapidly, so we can expect this product to evelve significantly over time, but it already does its job well.
For a more complete description, see my blog post:
http://activerain.trulia.com/blogsview/4401929/a-peek-at-the-future---realtybeacon