Abstract: A multiple-RF channel wireless security system has expanded monitoring and control capacity without a concomitant increase in the number of available RF channels. At least one primary condition-responsive monitoring and RF signaling device having a first range of values for the parameter being monitored has an associated secondary condition-responsive monitoring device having a second range of values for the same parameter connected in series with the primary device. The secondary device may operate in conjunction with or independently of the primary device. When operating in conjunction with the primary device, the secondary device supplements the primary device by providing a second range of parameter values, and may, for example, provide back-up or "fail safe" operation of the primary device. When operating independently of the primary device, the secondary device provides expanded monitoring and control capabilities of the security system while preserving the number of RF channels.