Includes (1) Built-in temperature sensor and (1) input for a remote sensor. Can accept one remote temperature sensor..... Whether it is a residential or commercial application, EnviroAlert provides the flexibility to simultaneously monitor temperature in one or more critical environments (sensor probes sold separately). With a designated output relay for each zone, EnviroAlert will activate alarms, dialers, transmitters, etc Part# E-003-0010 Required for interconnecting hardwire alarm control.