Emergency transporter armband

From Memory Alpha, the free Star Trek reference

An emergency transporter armband is a device used by Starfleet personnel during an away team mission to remotely activate the transporters of a starship or runabout for an immediate beam-up in the event of a dangerous situation where verbal communication is not possible, preventing a request for transport in normal circumstances. The armband comprises a type-7 phase discriminator and a subspace emitter. (TNG: "The Best of Both Worlds")

Geordi La Forge modified several transporter armbands in late 2369 to produce a subspace isolation field to protect the crew aboard the runabout from the effects of a temporal fragment. (TNG: "Timescape")