The good news is that these sensors are affordable. The price varies depending on their capabilities, but generally they’re €10-30 per beacon.
Using a Bluetooth connection provides them with real independence. As opposed to wi-fi, a beacon doesn’t need an internet connection. It also covers a broader range (up to 450 meters, depending on the model) than does NFC (Near Field Communication), which limits exchanges among peripheral devices at distances of 10 cm or less.
Another advantage is that a beacon consumes very little energy. It uses standard Bluetooth Low Energy, an efficient version of Bluetooth that allows devices to remain powered longer.