The Cooper echo was devised by Mr. Peter Cooper of Vancouver, British Columbia, Canada. The concept behind the Cooper echo is, simply stated, information passed to the partner of the declarer, or the dummy, that the contract will be made. This is the only information passed by the declarer, perhaps for the reason of assuring the partner that the contract will make.
Note: Any additional information about Mr. Peter Cooper, especially contributed photographs, would be greatly appreciated.
Parameters of the Concept
The Cooper echo does not automatically establish a claim in any form by the declarer of a certain number of tricks and/or overtricks. The concept is shown in the following diagram:
The contract is 3 No Trump by West, the declarer, and the lead by North is the 
3, which is explained as the fourth best from the longest and strongest suit. It is immediately evident that West does not have a 5-card Spade suit since the 2 is revealed in the dummy, or East. The declarer realizes that the defenders can take the first four tricks, but then must concede nine tricks.
In order to comfort, assure, and satisfy East, who sits as the dummy, that the contract is secure, the declarer performs a Cooper echo in the following manner. When the 3 is led, the declarer will call for the 6 from the dummy.
On the second trick, the declarer will play the 2, thus completing the Cooper echo, and informing the dummy that as soon as the Spades have been depleted, the remaining tricks will be won to fulfill the contract.
If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.