An apparatus for identifying failed or suspect RF transmitting devices while the devices are in normal operation transmitting over-the-air RF signals. The apparatus comprises an RF signal sensor receiving the RF signals from at least one of the devices that are mobile or portable. The sensor is responsive to the received RF signals. An analyzer determines RF frequency characteristics of the received RF signals from the at least one transmitting device, determines the respective identifier of the at least one transmitting device from the received RF signals, and uses the identifier from the received RF signals to correlate the RF frequency characteristics of the particular one of the transmitting devices. A graphical user interface displays at least one RF frequency characteristic in a form that can be used to identify transmitting devices that have failed and transmitting devices that are suspect.