The present invention relates to a personal property alarm system for monitoring the security of personal property using two-way coded radio signalling. The system comprises an alarm unit to be fixed to an item of property to be protected and a personal unit to be carried by a property owner. The alarm unit and the personal unit each comprise a transceiver to transmit and receive signals between each other. The alarm unit also comprises a motion sensor that is activated by predetermined movement of the property. The personal unit is operable in an alarm mode in which an alarm is activated to alert the property owner. The alarm unit is normally operable in a standby mode and is switched from the standby mode to an emergency mode when the motion sensor is activated. The personal unit alarm mode is activated when its transceiver receives an emergency signal from the alarm unit or when no standby signal has been received from the alarm unit. A personal unit may be tuned to communicate with a plurality of alarm units and/or a plurality of other personal units.