Hong Kong Exchanges and Clearing (HKEx) is acting to ensure that erroneous transactions - in which the wrong bid or asking price is input - are avoided. 'We are requiring all brokers to turn on the price-alert mechanism or to install a price-alert mechanism if they haven't built one into their broker supply system,' a HKEx spokesman said. The exchange would 'take appropriate action' if brokerages failed to activate or install the mechanism, according to the spokesman. This requirement comes in response to a spate of erroneous trades which jolted the markets at the end of last year. Most recently, on December 14, the Hang Seng Index plunged 344 points at the opening bell after a sell order on HSBC was entered at HK$106.50 - HK$9.50 below its previous closing price. Yesterday the exchange also announced that next Monday it would introduce two new order types to AMS/3, its third generation Automatic Order Matching and Execution System, to enable stock investors to place orders more efficiently. The new order types are Enhanced Limit Order (ELO) and Special Limit Order (SLO). The ELO will allow investors to match up to two different price queues at the same time by placing a single order. An SLO is a market order that can match the best price queue and the second best queue one spread away, as long as the traded price is not worse than the input limit price. The functions also increase the range for order prices and lift the maximum order size. 'We are taking advantage of AMS/3's wide range of functions to give market participants more flexibility and increase their operational efficiency when placing orders,' said Lawrence Fok Kwong-man, the exchange's deputy chief operating officer.