Split the working area by warning card before starting work, to avoid damage caused by entrance of passersby.

用警示牌将工作区域分隔起来，以防过路者闯入造成损伤。

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Or it knows you are a compulsive shopper: it can flash a warning on your credit card balance as you consider another purchase.

CNN: The wave of wearable computers

The paranoid fringe has been warning since the Visa card was introduced in the 1950s that it provides big business with a chilling way to snoop on our most intimate shopping habits.

FORBES: Voyeurism for Profit

In soccer, a yellow card is given as a warning to a player for an egregious violation of the rules.

NPR: Soccer Referee Punched By Player In Utah Dies