On selected products you will sometimes see some are marked "potentially lower price". You can choose to activate the discount on the items that are part of the campaign by using an on/off button which is located at the top of the product view page, the product page and in the basket.
If the item you wish to buy is part of the campaign and you have met the requirements to activate the discount and turned the function to "on", the new lower price will follow you all the way to the check out.
Please note that the discount is only valid if all requirements are met.
The requirements are always listed next to the on/off button.