A faraday cage or faraday pouch blocks electric radio. For example a cellphone will not be able to communicate with the base station if you wrap it aluminium f

A faraday cage or faraday pouch blocks electric radio. For example a cellphone will not be able to communicate with the base station if you wrap it aluminium foil and the new car fobs work similar. The fob just needs to be in close distance to the car for someone to open the door or starting the car. A relay attack puts two radio devices between the car fob and the car, so thieves can open and start a car just by relaying the radio signal to the car fob behind the closed door. A replay attack will record the radio signals transmitted between fob and car and just replay them. And both attacks are absolutely possible. You can find videos on youtube for both.