Complex sentence: Small gadget transmitters do not need to know what somebody is transmitting at the frequency, only to monitor channel occupation by radio receiver chips analog RSSI (Received Signal Strength Indication) to know when not to send.
Split into simpler sentences: Small gadget transmitters do not need to know what is being transmitted. There is only a need to monitor channel occupation by radio receiver RSSI (Received Signal Strength Indication) to know when not to send.