Faraday Bag for Cell Phones vs. Faraday Bag for Car Keys: Which One Do You Need? With smartphones and keyless cars becoming part of everyday life, protecting wireless devices from unwanted signals is becoming more important. A faraday bag for cell phones and a faraday bag for car keys may look si milar, but they are designed for different purposes. Choosing the right one depends on what you want to protect and how you use it. Quick Answer: faraday bag for cell phones is designed to block wireless signals from reaching or leaving your phone when it is properly enclosed. It can be useful when you want to reduce unwanted wireless communication, tracking, or remote access attempts. A faraday bag for car keys, on the other hand, is mainly designed to shield key fobs from receiving or transmitting radio signals that can potentially be exploited in relay attacks. If you want protection for your phone, choose a phone-sized Faraday bag. If your main concern is your vehicle's key fob, c...