Scouters are devices that measure power levels in Dragon Ball Z. Judging from the color it should be Raditz’s scouter however Raditz had red led at the muff. Raditz’s scouter was constantly used upon his arrival on Earth. Raditz used his scouter to see the power levels of a Farmer, Piccolo and finally Goku.
During his fight with Goku and Piccolo, Raditz went by his scouter’s power readings, causing him to underestimate them. After being delt a fatal blow, Raditz used his scouter to transmits Piccolo’s description of the Dragon Balls back to Vegeta and Nappa.