Method for bidirectional radio communication in an alarm system, surveillance or security system, installed at a site to be monitored and comprising on the one hand a central module forming a gateway and on the other hand at least one peripheral module, said modules each having an independent power supply, able to switch from an active or alert state to a deactivated or standby state with a low power consumption and vice versa, said or each of the peripheral modules being in discontinuous synchronous or asynchronous radio connection with the gateway, and the transmissions in the form of messages with defined structures only occurring between said gateway and the peripheral module or modules, over at least two dedicated radiofrequency channels, namely at least one communication channel which is normal for the synchronous or servo peripheral module(s) and an emergency communication channel for the asynchronous, disconnected or not yet synchronised peripheral module or modules, the gateway ensuring the management of the method and functioning of the peripheral module or modules and being used as a frequency and time reference for the system, the exchange of messages between the gateway and peripheral module or modules being performed in consecutive and contiguous time frames, dividing the time in a continuous and similar manner on said at least two transmission channels, the method being characterised in that each frame has a duration of less than 1s and is subdivided into five successive time windows (A, B, C, D, E) of similar duration; in that it consists on said at least one normal channel of - authorising the emission of the peripheral module or modules towards the gateway during the two first windows (A and B), due to a message via peripheral module; - verifying at the gateway during the third window of each frame the existence of a possible spontaneous emission or one or more peripheral module(s) during at least one of the two first windows (A and B) of the following frame; - authorising the emission of the gateway to one, several or all of the peripherals during the fifth window; - in that the use of the fourth window is managed in a dynamic manner and in real time by the gateway, each message received by the gateway or each peripheral module triggers the emission back towards to the transmitter module of an acknowledgement message, in that the gateway carries out during the third window of each frame, at least during a limited period at the beginning of said window, a measurement of the level of intensity or power of the radio signals received, RSSI, at least on the emergency channel, and in that said gateway is activated in reception, at least during a limited period at the beginning of the two first windows (A and B) of the following frame, when said measured level, RSSI, is greater than or equal to a predetermined threshold value, RSSI min, each peripheral module wishing to emit spontaneously during a given emitting frame during the third window of the preceding frame, in particular at least during a limited period at the beginning of said window a radio signal of sufficient power that the RSSI level measured by the gateway is greater than RSSI min. - authorising the emission of the peripheral module or modules towards the gateway during the two first windows (A and B), due to a message via peripheral module; - verifying at the gateway during the third window of each frame the existence of a possible spontaneous emission or one or more peripheral module(s) during at least one of the two first windows (A and B) of the following frame; - authorising the emission of the gateway to one, several or all of the peripherals during the fifth window; - in that the use of the fourth window is managed in a dynamic manner and in real time by the gateway, each message received by the gateway or each peripheral module triggers the emission back towards to the transmitter module of an acknowledgement message, in that the gateway carries out during the third window of each frame, at least during a limited period at the beginning of said window, a measurement of the level of intensity or power of the radio signals received, RSSI, at least on the emergency channel, and in that said gateway is activated in reception, at least during a limited period at the beginning of the two first windows (A and B) of the following frame, when said measured level, RSSI, is greater than or equal to a predetermined threshold value, RSSI min, each peripheral module wishing to emit spontaneously during a given emitting frame during the third window of the preceding frame, in particular at least during a limited period at the beginning of said window a radio signal of sufficient power that the RSSI level measured by the gateway is greater than RSSI min.