Direct remote identification (Remote ID) is a broadcast by the drone that transmits identification data during flight: the UAS operator registration number, the drone's serial number, its position, height and speed, and the pilot's location. The data can be received with an ordinary smartphone.
The function is required on class C1, C2 and C3 drones. Its purpose is simple — to let the authorities identify who is flying while the flight is in progress. That is why the operator registration number must be uploaded into the drone's identification system before the first flight.