Players are required to alert and announce special system agreements. In online games, these are made by the player making the call. A major revision of the requirements is now in effect.
A summary of the common changes is in the January issue of the ACBL Bulletin, p35. The full document: https://web2.acbl.org/documentLibrary/play/AlertProcedures2.pdf
A few examples of some changes …
Pre-alerts. Before auction begins on first board of a round, you must pre-alert if your system includes one-level bids that are not natural. Examples: “We play 1C could be short – may be only one”; “We play a strong 1C opening bid, may not have clubs”)
Alert a direct cuebid that is not Michaels.
Alert a new minimum level suit bid by an unpassed hand that is non-forcing.
Announce the suit of a transfer bid. Eg: 1NT-2H, announce “spades” not “transfer.
Announce the HCP range of any 1NT opening bid