A five-day, invitation-only test of online betting begins Thursday.
Technology companies working with the Atlantic City casinos tell The Associated Press they intentionally set their digital fences slightly away from the edge of New Jersey's borders.
The result will be small no-play zones that gamblers will have to leave temporarily if they want to bet online.
The width of the zones will vary. Regulators say someone who is shut out of one casino's site might be able to access another's.
The tech companies say they're erring on the side of caution to prevent the casinos from being fined for allowing unauthorized gamblers.