A Beacon is a small transmitter that sends signals on the Bluetooth low-energy standard with a range of up to 40 meters. Beacons send a signal at a specific time interval that can be assigned by the correct receiving device. In most cases, the device is a smartphone or tablet with the corresponding app. In the signal, an ID is transmitted with which each beacon can be identified. Meanwhile, a distinction must be made between iBeacons (Apple) and Eddystone beacons (Google). Eddystone beacons, in contrast to iBeacons, can send a URL. In so-called audio beacons, no physical device is meant, but an audio signal inaudible to the human ear. Information similar to a watermark is modulated into the signal, for example about the location. The technology is therefore also called audio watermarking.