Communication unit (SYST) based on a determined protocol, said communication unit (SYST) comprising: - a master entity (ENT_MAS); - a slave entity (ENT_SLV) able to communicate with a vehicle according to a UHF or LF protocol; - said master entity (ENT_MAS) and said slave entity (ENT_SLV) being able to communicate by bluetooth, bluetooth low energy, BLE, or NFC protocol, - said slave entity (ENT-SLV) being able to take the following states of the bluetooth or bluetooth low energy, BLE, protocol: - idle, in which the slave entity (ENT_SLV) neither receives nor emits signals, and is not connected to any entity; - discoverable, in which the slave entity (ENT_SLV) periodically emits presence signals (sig_pres); - connected, in which the slave entity (ENT_SLV) is connected to the master entity (ENT_MAS); - said slave entity (ENT_SLV) being able to take the following states of the NFC protocol: - an active state or reading mode; - a passive state or emulating mode; - and said slave entity (ENT_SLV) also being able to take the following state: - listening mode, in which the slave entity (ENT_SLV) is able to receive signals from the vehicle by UHF or LF protocol the communication unit being such that when the master entity (ENT_MAS) and the slave entity (ENT_SLV) are connected according to the bluetooth, bluetooth low energy, BLE, or NFC protocol, the master entity (ENT_MAS) is able to dispatch alarms for activating the listening mode state to the slave entity (ENT_SLV), each of said activation alarms corresponding to an activation hour value. - a master entity (ENT_MAS); - a slave entity (ENT_SLV) able to communicate with a vehicle according to a UHF or LF protocol; - said master entity (ENT_MAS) and said slave entity (ENT_SLV) being able to communicate by bluetooth, bluetooth low energy, BLE, or NFC protocol, - said slave entity (ENT-SLV) being able to take the following states of the bluetooth or bluetooth low energy, BLE, protocol: - idle, in which the slave entity (ENT_SLV) neither receives nor emits signals, and is not connected to any entity; - discoverable, in which the slave entity (ENT_SLV) periodically emits presence signals (sig_pres); - connected, in which the slave entity (ENT_SLV) is connected to the master entity (ENT_MAS); - idle, in which the slave entity (ENT_SLV) neither receives nor emits signals, and is not connected to any entity; - discoverable, in which the slave entity (ENT_SLV) periodically emits presence signals (sig_pres); - connected, in which the slave entity (ENT_SLV) is connected to the master entity (ENT_MAS); - said slave entity (ENT_SLV) being able to take the following states of the NFC protocol: - an active state or reading mode; - a passive state or emulating mode; - an active state or reading mode; - a passive state or emulating mode; - and said slave entity (ENT_SLV) also being able to take the following state: - listening mode, in which the slave entity (ENT_SLV) is able to receive signals from the vehicle by UHF or LF protocol the communication unit being such that when the master entity (ENT_MAS) and the slave entity (ENT_SLV) are connected according to the bluetooth, bluetooth low energy, BLE, or NFC protocol, the master entity (ENT_MAS) is able to dispatch alarms for activating the listening mode state to the slave entity (ENT_SLV), each of said activation alarms corresponding to an activation hour value. - listening mode, in which the slave entity (ENT_SLV) is able to receive signals from the vehicle by UHF or LF protocol the communication unit being such that when the master entity (ENT_MAS) and the slave entity (ENT_SLV) are connected according to the bluetooth, bluetooth low energy, BLE, or NFC protocol, the master entity (ENT_MAS) is able to dispatch alarms for activating the listening mode state to the slave entity (ENT_SLV), each of said activation alarms corresponding to an activation hour value.