Bluetooth Low Energy, or BLE, is a short range wireless standard designed for low power communication over roughly tens of metres. It is widely used for beacons and for detecting nearby devices.
The longer version
Bluetooth Low Energy is a variant of Bluetooth built to sip power. A device can broadcast small packets for long stretches without draining a battery, which is why BLE became a common choice for beacons and presence detection. The Bluetooth SIG maintains the standard.
Its range runs to roughly tens of metres, depending on the radio class and the environment. Walls, bodies, and interference shorten it. That reach is generous enough to notice a phone across a room, which suits proximity use where a deliberate tap would be too restrictive.
In a proximity payment setting BLE is one way to broadcast a provider's presence. The phone detects the signal and reports it, and the server resolves the nearest pairing. The BLE link itself never carries the transaction.
The Parousya method
Bluetooth Low Energy is one of the signals the Parousya method can use to sense presence. The patent is not tied to a single radio, so BLE serves where room scale detection at low power is the right fit.