The following information was taken directly from the United States Coast Guard blog post titled "Engine Cut-Off Switches" on May 21, 2021.
"On April 1, 2021 a new federal law goes into effect that requires the operator of a boat with an installed Engine Cut-Off Switch (ECOS) to use the ECOS link. The link is usually a coiled bungee cord lanyard clipped onto the operator's person, Personal Floatation Device (PFD) or clothing and the other end attached to the cut-off switch, but there are plenty of variations on the market, including electronic wireless devices. The law applies on all "Navigable Waters of the US".
When an operator is wearing a link while underway, the engine will cut-off if the operator is separated from the operating area, an occurrence that can happen if the operator is ejected from the vessel or falls within the vessel. The shutdown of the engine is essential for safety reasons. If the operator is ejected from the vessel, the shutdown may prevent the operator from impacting the vessel's spinning propeller, and may aid the operator in safely returning to the drifting vessel.
The law applies to "Covered Recreational vessels" which means any motorized boat with 3 or more horsepower that is less than 26 feet in length and takes effect on April 1, 2021.
Operator Requirement: An individual operating a covered recreational vessel shall use an engine cut-off switch link while operating on plane or above displacement speed."
For more information reference the United States Coast Guard Boating Responsibility site at https://uscgboating.org/index.php.