Trailing stop

The help page says the tool checks, when a new quote arrives, whether the open position's profit in points has reached the distance the trader set. It then places or moves a stop loss that far from the current price. If price moves back, the stop stays where it is. Only one trailing stop can be set on a position, and it is processed no more than once every ten seconds. Because it runs in the platform, it does nothing while the platform is closed. A stop loss already written to the server can still trigger. MetaQuotes lists a trailing stop on MetaTrader 4 as well. It is an automation of a stop move, not a promise that the profit is locked.