An outage of a cellular base station is detected by a neighboring base station when a beacon signal previously stored by the neighbor in respect of the base station being monitored is compared with the result of a subsequent search for that signal and found to have deteriorated or ceases to be detected. If the search identifies such an event, the search is repeated at a shorter interval and an outage is reported to a management center if the base station also fails to be detected on subsequent consecutive sampling cycles. This avoids false alarms from reboots and other transitory losses of signal that would be caused by an outage report based on a single loss of signal.