A method of supervising intruder alarm systems, each alarm system comprising a plurality of alarm sensors and at least one gateway communicating with a remote alarm receiving center. The method includes the steps: a) receiving in a first intruder alarm system radio signals transmitted from a second intruder alarm system, b) transmitting from said first intruder alarm system information relating to the received radio signals to said remote alarm receiving center, c) analysing in said remote alarm receiving center information received from intruder alarm systems to identify at least one first intruder alarm system and at least one second intruder alarm system capable of exchanging information via radio signals, d) transmitting from said remote alarm receiving center control signals to said first intruder alarm system and to said second intruder alarm system to operate as a supervising system by monitoring radio signals from the other intruder alarm system operating as a supervised system, e) observing in either one of said first intruder alarm system and said second intruder alarm system absence of the monitored radio signals, and f) transmitting from a supervising alarm system an alarm signal when absence of said monitored signals is detected.