An unattended sensor is provided for use in a surveillance system. The sensor is generally comprised of: a detector that generates an electrical signal in response to a physical stimulus proximate to the sensor; a signal processor adapted to receive the electrical signal from the detector and operable to generate an event message based on the electrical signal; a transceiver operable to send and receive messages over a wireless radio link; and a channel access mechanism operable to negotiate access to the radio link in accordance with an access protocol, where the access protocol is employed by radios and other communication devices in the system.