this example corresponds to a mode of use in which the terminal controls entry into a controlled area . fig1 shows : a terminal 1 which includes a contactless reader having an antenna 2 under a cover that is transparent to electromagnetic radiation , and a contactless medium in the form of a smart card 3 incorporating a microcircuit 4 communicating with the outside world via an antenna 5 and optionally a connection interface 6 with electrical contacts . the terminal 1 is in the form of a cabinet alongside a passageway blocked by a three - legged turnstile 9 . the terminal 1 further includes . a display 7 and a loudspeaker 8 for imparting information to a user , and a collection device essentially consisting of a collecting chute 10 into which the user slides or throws the smart card at the invitation of the display 7 and the loudspeaker b . standard means , not shown , for extracting the electrical power required for it to operate from the electromagnetic signal received by its antenna 5 , standard means , not shown , for transmitting and receiving data via the antenna 5 , a logic circuit 11 for processing the data ( for example a microprocessor and an associated program ), in particular for effecting a payment operation and securing the data exchanged with the terminal 1 , and a non - volatile memory 13 containing transaction data . a credit is stored in a portion 14 of the memory 13 . some credit units are electronically canceled by the circuit 11 to show that their value has been used up . a second portion 15 of the memory 13 contains an identifier , for example the user &# 39 ; s social security number . fig2 is a flowchart of one example of the method of the invention . when a user with a smart card 3 approaches the terminal 1 , the contactless smart card reader detects the presence of the microcircuit 4 . this is step 17 in fig2 . when the card 3 receives the signals transmitted by the antenna 2 , it transmits data to the reader in the terminal 1 . in step 18 the reader in the terminal 1 reads the transaction data contained in the memory 13 of the card 3 . the reader then performs a test to determine if the card is valid ( step 19 ). the test verifies if the card 3 corresponds to the intended purpose of the terminal 1 : the card 3 may not correspond to the transport company operating the terminal 1 . in this case , the card is refused but is not retained . a message on the screen 7 and a sound signal or message reproduced by the loudspeaker 8 indicate that the card does not authorize access ( step 20 ). if the card is valid , the reader in the terminal 1 modifies the credit stored in the portion 14 of the memory 13 ( step 22 ). it causes the circuit 11 to write data . after this writing , the card may not be valid for a subsequent journey . the reader in the terminal 1 tests whether the card is valid for another journey by comparing the remaining credit to a predetermined amount ( step 23 ): if the card is still valid for another journey , or another use , the reader authorizes entry / exit ( step 24 ). the reader commands the unlocking of a latch which prevents the barrier 9 rotating . it displays on the screen 7 a message 25 indicating that the use of the service has been accounted for and inviting the user to pass through the barrier . the display can be replaced by the lighting of a green lamp or any other visual and / or audible and / or mechanical signal . in this instance , all that remains is for the user to pass through the barrier . if the card is not valid for another journey , the user is invited to insert the card into the chute 10 to return it to the transport company ( message 27 , step 28 ). this is because , in this example , the terminal 1 controls entry to a controlled area and the user is invited to return the card before making the journey . in return the user is issued a ticket 26 indicating the legitimate nature of his situation during the journey . a message on the screen 7 and / or a sound message reproduced by the loudspeaker 8 then indicates that the card must be given up by inserting it into the chute 10 ( step 28 ). at the same time , the terminal 1 prepares to retain the card . meanwhile , the barrier remains locked . a test verifies whether the card has been returned ( step 29 ): if it has , a message 30 on the screen 7 and / or an audible message reproduced by the loudspeaker 8 invite ( s ) the user to take the ticket 26 and pass through the barrier 9 . the barrier 9 is then unlocked ( step 24 ). if it has not , the barrier 9 is not unlocked . at the end of a predetermined time the terminal 1 reverts to step 1 to detect the card of another user . in another mode of use , the terminal 1 controls exit from the con - rolled area . in this case , users are invited to hand in their card at the end of the journey , but there is no need to issue a ticket 26 in exchange . fig3 shows the construction of the terminal 1 in more detail . its main components include a printer 36 , a contactless reader 31 connected to the antenna 2 and a microprocessor 32 . to prevent entry of foreign bodies into the chute 10 , the chute is provided with an access door 33 . the microprocessor 32 opens the door 33 only when it receives from the reader 31 information indicating the presence of a card 3 whose credit has just been used up and is therefore to be handed in . in all other cases , the door 33 remains closed . for implementing the test of step 29 , the chute 10 has another door 34 further downstream and also controlled by the microprocessor 32 . the door 34 retains in the chute 10 a card 3 or any other object deposited therein . during this time , the nature of the object is tested . to this end , a detector 35 faces the chute 10 , slightly above the door 34 . the detector 35 can be a very simple device , for example an optical or infrared detector . it can also be an antenna of the same type as the antenna 2 and which is coupled to the reader 31 to read the memory 13 of the deposited card . if the presence of a card 3 is detected in the chute 10 , the processor 32 authorizes user entry or exit , opens the door 34 and causes the printer 36 to deliver a ticket 26 . all the operations are timed and synchronized so that they can be efficiently perceived by the user . if no card 3 is detected in the chute 10 , the microprocessor 32 leaves the door 34 closed and does not unlock the barrier 9 . if a foreign object has been inserted , it remains in the chute 10 and the door 33 remains open until a user removes the foreign object and deposits a card . a routing device 37 controlled by the microprocessor 32 can optionally divide cards into two categories . to remedy the insertion of foreign objects , the routing device 37 can also separate cards from other objects thrown into the chute 10 . to this end , the receptacle of the terminal 1 includes two hoppers 38 and 39 . the cards can be stored loose in these hoppers or stacked to facilitate their re - use . in practice the entry slot above the door 33 is shaped to facilitate inserting the card . the opening can be wider than the entry slot of a magnetic stripe reader because its guide function is less precise , to facilitate fast insertion of the card . the two doors 33 and 34 are preferably actuated so that opening of the door 34 is followed a second test by the detector 35 to verify that the card is no longer present before authorizing re - opening of the door 33 . this prevents removal of cards by so - called “ fishing ” methods . cards valid for a single journey ( single cards ) do not need to be recharged and can be recycled without rewriting their memory . the other tickets are recharged by writing a new value into the microcircuit 4 . a secret key is generally required for recharging the microcircuit 4 . the security precautions in respect of the secret key are simpler because the value is recharged only by employees of the company owning the terminal 1 . the recycling mode is preferably adapted to suit particular operating conditions . in the situation where only single cards are recycled and then dispensed automatically , the collected cards are stacked in the hoppers without recharging their value . they are recharged at the time they are sold . for manual distribution to ticket offices of stations equipped with a reader for recharging their value , the cards are stacked in boxes without recharging their value . their value is recharged at the time they are sold . for distribution by external resellers , who have no means of recharging their value , the tickets have their value recharged by a secure dedicated equipment unit belonging to the transport company . the cards can be stacked any way around , unlike magnetic stripe cards , which simplifies the mechanism in the terminals .