Method for detecting the absence of a physical element in a geographical zone, and associated system

A transmitting device including:

• a transmitter;
• at least one processor;
• and
• at least one non-transitory computer readable medium comprising instructions stored thereon which when executed by the at least one processor configure the transmitting device to:
• obtain an amount of electrical energy stored from light energy,
• compare the amount of electrical energy stored with a given threshold, and
• transmit, with the transmitter, in response to the amount of stored electrical energy being greater than said threshold, a message called “information message”, representative of said threshold overrun, by ambient backscattering and using the stored electrical energy.

A receiving device including:

• a receiver;
• at least one processor;
• and
• at least one non-transitory computer readable medium comprising instructions stored thereon which when executed by the at least one processor configure the receiving device to:
• receive, with the receiver, an ambient backscattering a message called “information message”, representative of an overrun of a threshold given by an amount of electrical energy stored by a transmitting device, said information message being transmitted by said transmitting device, and
• transmit, to at least one communication terminal, a message called “alert message”, representative of said threshold overrun.