The card simply sits in front of up to 3 contactless bank, travel or ID cards to protect them against daily issues from daily Accidental Payment evidenced on transport (such as TFL), retail POS and venues as well as ID theft from the e-skimming of the data held on the chip through the use of hand held smartphone apps or card reader devices.
 
Standards card size 85mm by 54mm. Passive Technology. No batteries required. No circuits that can break. No lights that light up. No power needed or stored.