(via), a tool to prevent yourself from being tracked:

The mobile phone pouches "Silver" and "Copper" act as Faraday cages, completely shielding the phone and preventing it from sending or receiving signals. (...) The pouch prevents the user being located or having their movements followed. Even turning off the phone cannot always guarantee this. In the possession of this personal radio blocker, a mobile phone owner can decide whether they would like to be in a spatial data model or not.A simple piece of fabric in the form of a pouch turns off a highly intergrated and technically complex appliance.The constant space-related data exchange becomes identifiable by being interrupted.