A Control recommends an action (denial) to the card processor based on the merchants, transaction types, location types and spend limits you set for that card. For example, say you want to be able to use your card for any type of in-store transaction at any merchant type, but you do not want your card used for Online or Mail/Phone order transactions, regardless of the merchant type and not for any purchase over $1000.00.
An Alert notifies you based on the Controls you set. You can choose to get alerts every time your card is used, only for preferred transaction categories or only when your card is attempted to be used for transaction types or merchants you have chosen to block. You can also choose to receive an alert any time a transaction occurs over a certain dollar amount.