A Rubindium-transponder transporter recall bracelet (sometimes shortened to Rubindium-transponder) is a device that allows an individual to send a transporter command to a transporter activating the remote transporter recall command.
Transporter scramblers will block the signal from a Rubindium-transponder.
In the 2268 Starfleet Intelligence was issuing these bracelets to their operatives to be used as an emergency extraction device. Lieutenant commander Bridget McLellan used one while she was on the Gorn Hegemony planet of Seudath. She was happy that the device had worked as promised while escaping from the Klingon safe house. (VAN - Declassified novella: The Stars Look Down)