Abstract: A portable telephone communications system has a portable telephone terminal (300) and a repeater unit (100), and a remote receiver unit (200), wherein the repeater unit (100) includes a main power supply control device which includes detection means triggered by a signal from the telephone terminal arising on receipt of an incoming call, and including infra-red transmission means for transmitting the signal as a frequency-modulated signal to the remote receiver unit; the remote receiver unit (200) includes an infra-red receptor, demodulation means (205) and means for outputting the demodulated signals as audible voice signals, and further comprises a noise level comparator (209d) which compares the voltage of noise generated when no infra-red signals are received with a predetermined level and delivers an output signal when said voltage exceeds the predetermined level, and a time counter (210) which outputs a reset signal when the output from the noise comparator has been generated for a predetermined time i