The TWS contains two checks to limit the possibility of clients entering trades at prices which are substantially inconsistent with that of the current market. 

Under the first check, stock buy orders which are 10% above the prevailing NBBO ask price will be automatically rejected by IBKR as will stock sell orders which are 10% below the prevailing NBBO bid price.  In the case of options, IBKR's automatic rejection threshold percentage for both buy and sell orders is 20%.  When an order violating these parameters is transmitted, it will be rejected and a TWS pop-up window will be displayed with the following warning message: "Limit price too far outside NBBO" or "This order is not accepted.  The limit price cannot be more than 10% through the NBBO.".

The second check relates to orders which are transmitted at prices which do not violate the parameters set by IBKR as outlined above, but which do violate parameters established by the account holder.  Here the account holder is able to establish Precautionary Settings by selecting the Order and then Configure Order Presets menu options from the TWS. This will open up a window providing for the creation of price thresholds set in terms of percentage or the number of ticks outside of the NBBO (settings may also be defined in terms of share/contract quantity or total dollar value of trade).  When an order violating the account holder's parameters is transmitted, it will be rejected and a TWS pop-up window will be displayed with the following warning message: "The price specified would violate the percentage constraint specified in the default order settings.  Do you really want to submit this order?"  Unlike in the case of the check set by IBKR, the account holder has the option of overriding their own settings and transmitting the order by clicking on the "Yes" button.