Recent devices include Bluetooth 4 which is able to run in a low energy (LE) mode and ping out a beacon running on a small battery for up to a few years. I purchased a few samples from Estimote that look like this:
It's also possible to use a Raspberry Pi with a USB bluetooth 4 dongle (I bought a Targus one for $40) to make a beacon. I followed instructions and it worked out of the box.
With this software you can make a beacon that emulates either Apple's AirLocate samples or beacons from any other vendor including Estimote, Radius, RedBear Labs, TwoCanoes or any others.
To scan for beacons, (without writing a specific app), there are a few iOS apps including the Estimote app and "Locate iB". On MacOS there's an app that can find any beacons in range called iBeaconScanner:
By pretending to be an Estimote beacon you can use their app to scan too:
All good fun. I'm sure we'll see these things everywhere within the next few years.