According to one aspect, embodiments herein provide a PoE sensor comprising a housing, sensing circuitry disposed within the housing and configured to detect a physical phenomenon outside the housing, at least one internal power source equipment (“PSE”) circuit disposed within the housing and configured to transmit PoE power and data to at least one downstream sensor, and powered device (“PD”) circuitry disposed within the housing, coupled to the sensing circuitry and the at least one internal PSE circuit, and configured to receive PoE power and data from at least one element of PSE external to the housing, transmit PoE power to the sensing circuitry to initiate operation of the sensing circuitry, and transmit PoE power and data to the at least one internal PSE circuit to initiate transmission of PoE power and data to the at least one downstream sensor.