Don’t trust your kids to roam wild on a cruise ship? Neither does Royal Caribbean, which has unveiled an electronic bracelet that allows parents to track their movements onboard. The bracelets will work in conjunction with the cruise line’s new iPhone rental service, USA Today explains. All children will have to wear the bracelets, but only parents who rent the Royal Connect phones—which cost $17.50 and work only onboard—will be able to track them. (More cruise lines stories.)