An identification system comprising a reader (10) including a first signal generator (12) for generating a first signal (F1) which is radiated by an antenna (17). An identifier (11) includes an antenna (20) receiving the first signal for transmission to a signal modulator (32) which operates to modulate the signal in accordance with a preassigned code for the identifier. The modulated signal is then used to periodically unload or change the reactance of the antenna (20) which action in turn changes the reactance of the reader antenna and consequent voltage on the reader antenna (17). By detecting the change in the voltage on the reader antenna the code of the identifier is determined. Power drain is minimized and power is used efficiently by unloading during modulation and by changing reactance without changing load.

Chip cards that operate contact-free are supplemented by additional elements to enable remote transmission of data. Also, elements include sensors that enable the acquisition of physical, chemical or biological information from the environment of the card. Further, the card includes elements for storing electrical energy, electronic components for constructing an electronic oscillation circuit for the remote transmission and reception of data, as well as a switch accessible by a user for selectively connecting the energy storage elements to the electronic components thereby forming an electromagnetic oscillation circuit for the transmission of electromagnetic oscillations with information modulated thereon. In a preferred embodiment, one or both of the coils that are provided on the card are connected via the switch such that the coils serve as an antenna for the electromagnetic oscillation circuit for the remote transmission of data. In addition, the electronic oscillation circuit operates at a frequency which differs sufficiently from the frequency used in the short-distance transmission and also lies outside of the harmonics of the short-distance transmission so that a receiver of the information can differentiate merely on the basis of frequency, whether the remote transmission or the short-distance transmission is active.

An electronic identification and recognition system in which the recognition portion includes a voltage controlled oscillator which sweeps over a range of frequencies. The identification portion resonates at certain frequencies determined by a variable reactance in the resonant circuit in the identifier which is responsive to bits from a sequential data register. The bits result in the on-and-off switching of the variable reactance which modifies the resonant frequency in the identification portion or modifies the frequency of an oscillator in the identification portion. The changes and sequence of changes in the resonant frequency are detected and recorded by the recognition portion such that the internal code of the identifier is determined.

A device for recording a variable information in a programmable hub, for storing it and for restoring it without contact or electrical connection and without electric supply between the hub and information generator or the information readers. The generator or the readers comprise an oscillator or a power coil which supply the programmable hub with energy. The programmable hub restores the information by actuating an active loop which operates on a signal oscillator or on the readers. The invention is particularly applicable to dynamic coding.

A tone code identification system identifies a stolen computer every time the same is turned on. Police, on recovering a stolen computer, can call a central registry and transmit the tone code to reveal the identity of the rightful owner.