The HF CONTACTLESS cards use radio frequency, they are in fact also called RFID (Radio Frequency IDentifier) ​​or contactless cards.

Two devices are required to function: a smart card reader (active element) and a smart card (passive element).

When the reader is connected to the computer it generates a magnetic field and if a smart card is brought close to the reader (on average 5 centimeters) the card through the antenna transforms the magnetic field into current and thus powers the chip.

At this point the two devices are connected to each other and the data exchange is managed by the software.

The first cards worked at the frequency of 125 KHz (LF CONTACTLESS), but this type of technology is going into disuse as it is obsolete and in any case not very flexible, in many cases it uses a single string of data,

The most recent cards, but not the very latest ones, use a frequency of 13.56 MHz, the best known are NXP's MIFARE cards which have become a de facto standard.

They use various sectors, which can be used for different services: for example, a sector for access to the company, a sector for access to the canteen, one for access to coffee machines, etc. etc