A CS2 Doppler is one skin finish that comes in several visible forms. The base finish blends dark, metallic colours with streaks of red, blue, purple or black. Which colours dominate depends on the item's pattern index, and the community groups those outcomes into phases.
Doppler is best known on knives. It first shipped as a knife finish in the Chroma Case in January 2015, and a related finish called Gamma Doppler, which uses greens and blacks instead of reds and blues, arrived with the Gamma Case in June 2016. Both finishes have since appeared on more knife models and on a few weapons.
Why do Doppler prices vary so much?
The name in the inventory only says Doppler. It does not say which phase you got. The regular phases, numbered 1 to 4, sit close together in price, while the gem phases, Ruby, Sapphire and Black Pearl, can sell for many times more because far fewer pattern indexes produce them.
The Steam Community Market lists all Dopplers of one knife under one name, so buyers there rely on the inspect link and the listing image to spot the phase. Third-party marketplaces usually tag the phase for you. Always check the phase yourself before paying a gem price.
How do you check a Doppler phase?
Open the inspect link and look at the blade colours. A float checker tool reads the pattern index and reports the phase directly, which is faster and safer than judging by eye. Some phases look alike in low light, so a tool check protects you from an honest mistake by the seller and from a seller who hopes you will not look.
Float value still matters on a Doppler, but it matters less than phase. Doppler and Gamma Doppler have a float range of 0.00 to 0.08 in the item data, so they only exist in Factory New and Minimal Wear, and the phase is the first thing a buyer asks about.