To save energy, GRETA is not always active. The tracker switches between an active and a sleep mode.

If the tracker is resting and its position does not change, the tracker will enter a sleep mode. In sleep mode, GRETA does not transmit any signals. Only when the tracker is moved again does it switch back to active mode.

Depending on how long GRETA has been in sleep mode, it may take a while for the first position to be found. Why this is so you can read in the following article:

Why does it sometimes take longer for GRETA to find a position?