![Subspace force field](https://cdn.statically.io/img/static.wikia.nocookie.net/memoryalpha/images/4/4a/Subspace_force_field.jpg/revision/latest/scale-to-width-down/180?cb=20120629134803&path-prefix=en)
Three modified armbands in use, worn on one's left arm
An emergency transporter armband was 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 was not possible, preventing a request for transport in normal circumstances. The armband comprised 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")