A frac plug system for use at the end of well drill string in a fractured underground formation, including an elongated mandrel body, a nose cone, a mandrel head, and a sealing assembly; at least one sensor positioned on the nose cone, the sensor being optionally a temperature sensor, pressure sensor, pH sensor, or fluid composition sensor; a battery operated microcontroller located in the mandrel body, the microcontroller constructed and arranged to periodically read the data output of the sensor and store the data from the sensor; a transmitter constructed and arranged to transmit the stored data from the set of sensors to a receiver on a pup joint when the receiver is in receiving range of said transmitter, the receiver constructed and arranged to write the transmitted stored data to an electronic memory; and whereby the data may be retrieved from the electronic memory.